Archive for category: Java

Printing the pyramid pattern of stars is a common practice in learning any programming language. In this post, we will learn how to print the pyramid pattern of stars in Java. The program output for a pyramid of ten lines of stars is provided below.

My Computer$ java Pyramid
Enter number of lines: 10
         *
        ***
       *****
      *******
     *********
    ***********
   *************
  ***************
 *****************
*******************

Video lecture explaining how to print a pyramid of stars in Java

The following video provides a detailed talk on how to print a pyramid pattern of stars in Java.

Coming up with the solution

In the video above I discussed how we might draw a Pyramid pattern of stars in Java. I used loops to display the pyramid pattern of stars. I analyzed the problem from a problem-solving viewpoint and then wrote the code. 

Drawing the pyramid pattern is widely used in teaching programming courses because it requires some analysis of the problem before we directly jump into the code.  

Example

    *
   ***
  *****
 *******
*********

Notice in the pyramid above that we have 

1 star in the first line, 

3 stars in the second line, 

5 stars in the third line, 

7 stars in the fourth line, 

And finally, there are 9 stars in the fifth line.

The pattern is such that the number of stars increases in consecutive lines. Our target is to use a loop to go over each line and print the stars. 

Going over lines

In my code, I will use a variable named i, to go over every line of stars. That is, “i” will vary from 1 to 5 for the above example-pyramid contains five lines of stars. 

Finding the relationship between a line and how many stars to print

For such a pattern-printing problem, it becomes beneficial if we can come up with a relationship between a line number i  and how many stars we should print on that line. Let us try to find a connection between the line number and how many stars to print in that line. Let us iterate over the number of stars in the lines again.

When we are in line 1, we print 1 star. 

In line 2, we print 3 stars. 

When we are in line 3, we print 5 stars. 

So and so forth.

The question we are trying to frame here is, when we are in the ith row, how many stars will we print? 

The formula for the number of stars in a line

Notice that the number of stars to be printed = 2*the line number we are currently in minus 1.

That is, if we are in the ith line, the number of stars to be printed is 2*i-1. 

Let us check, if the hypothesis is correct for our running example. 

When we are in the first line, i=1. Therefore, the number of stars in the first line should be 2*i-1=2*1-1=1. Therefore, we print one star in the first line.

When we are in the second line, i=2. Therefore, the number of stars in the second line should be 2*i-1=2*2-1=3. Therefore, we print three stars in the second line.

When we are in the third line, i=3. Therefore, the number of stars in the third line should be 2*i-1=2*3-1=5. Hence, we print five stars.

If we keep doing these calculations, we will see that the formula for the number of stars in the ith line, 2i-1 is correct for any line. 

That is great! We have a formula for the number of stars for the ith line. 

How about the leading spaces

We have left out an important item in our analysis so far. Notice that, printing a pyramid of stars is not just printing stars in a pattern. What do I mean? In each line, we have some spaces before we start to print the stars of that line. The gap becomes smaller and smaller in subsequent lines. In the last line, there is no gap between the border and the first star of that line. These gaps in these lines are actually space-characters. That means we print some spaces before printing the stars in each line.

Let us analyze how many spaces we need to print before printing the stars in each line. That is, using the line number i, we will try to come up with a formula for number spaces in a line. 

Finding the relationship between a line number and number of spaces to print

You can use a paper and draw grids around the stars like the following one. Given that spaces are invisible drawing the grids will help us count the number of spaces in each line. 

Now, let us count the spaces in each line.

We have 4 spaces in line 1. 

There are 3 spaces in line 2.

We have 2 spaces in line 3

We have 1 space in line 4.

Line 5 contains zero space.

Notice that the number of leading spaces in a line is the total number of lines minus i, where i is the line number.

For example, let us take line 1. Here i=1. The number of spaces is 5-1=4. 

In line 2, i=2. The number of spaces in the second line is 5-2=3.

In line 3, i=3. The number of spaces in the third line is 5-3=2.

In line 4, i=4. The number of spaces in the fourth line is 5-4=1.

In line 5, i=5. The number of spaces in the fifth line is 5-5=0.

The formula for the number of spaces

Notice that for the ith line, if we subtract i from the total number of lines, we will get the number of leading spaces. Therefore, we can say, the number of spaces in line i is equal to n-i, where n refers to the total number of lines.

Summary of the analysis

Based on our analysis, we have come up with two things. 

If we are printing n lines of stars, then

1. The number of leading spaces in the ith line is n-i.
2. The number of stars in the ith line is 2*i-1.

We use these two pieces of information in our code.

Pseudocode

Let us write a pseudocode for the solution first. Pseudocode is an informal coding to help design the actual program.

I will ask the user about how many lines the pyramid should contain.

Let us say, the user enters the number of lines in a variable named n.

Then I will write a loop that will iterate n times. To iterate, I will use a variable i. Inside the loop, i contains in which line the program is. Therefore, based on our discussion earlier, we can print n-i spaces first, and then we will print 2*i-1 stars. I will make sure to write a new line after printing al the required stars in a line. Here is the pseudocode.

That’s it. We have the structure of the code. Let us go for coding.

The solution to printing a pyramid pattern

The code below provides a solution to printing a pyramid pattern. The program asks how many lines the pyramid should contain. Then it draws a pyramid containing a total number of lines provided by the user.

import java.util.Scanner;

class Pyramid{
  public static void main(String[] args){
    int n, i;
    Scanner scan = new Scanner(System.in);
    System.out.print("Enter number of lines: ");
    n=scan.nextInt();

    for (i=1; i<=n; i=i+1){
      int sp;
      for (sp=1; sp<=n-i; sp=sp+1){
        System.out.print(" ");
      }
      int st;
      for (st=1; st<=2*i-1; st=st+1){
        System.out.print("*");
      }
      System.out.println();
    }

  }
}

In the pyramid problem, we are given n, the number of lines as the input. We use a Scanner object to get the number from the user.

Then, we write a for-loop to vary the value of variable i, from 1 to n. 

Now, inside the loop, we will have to print the leading spaces. We write an inner loop to print (n-i) spaces. The loop variable is sp. sp will vary from 1 to (n-i). We will just print a space in each iteration of this inner loop.

After printing the spaces, we have to print the stars. The number of stars we have to print is 2*i-1. We use another loop that iterates 2*i-1 times. The loop variable is st. Inside this loop, we will print a star. 

Finally, after printing the spaces and the stars, we just write System.out.println() without anything inside the parentheses to print a new line. We are done with the code.

Save the file, compile it, and run it. Enjoy the program.

More exercises

Now that we know how to print a pyramid pattern os stars, we can use the knowledge to print other patterns. Write two programs for the following two patterns (Pattern A and Pattern B). The one on the right is slightly harder than the one on the left. Write the code for the left one first and then go for the right one. Enjoy!

Concluding remarks

The purpose of the post is to demonstrate not only to demonstrate how we can print the pyramid pattern but also to demonstrate how to analyze a problem before diving into coding. For most real-life problems, you will see that analysis of the problem and coming up with a sketch of code help write the code quickly. In the given problem, printing the pyramid pattern of stars, I could not write the code without really doing the analysis. I had to figure out how the pattern is changing from one line to another. We need analysis for that.

The summary is, 

1. Please analyze the problem you are trying to solve before starting to code.
2. Come up with a sketch of the solution on paper first.
3. Then go for coding. 

Many times, you will see that coding is the easy part. The analysis is a critical part of programming.

Anyway, if you haven’t subscribed to our website Computing4All.com and to the YouTube channel where we host our video lectures, please do so to receive notifications on our new articles and videos. Please do not hesitate to contact us via the comments section below. See you soon in another post.

Java has three types of loops: (1) for loop, (2) while loop, and (3) do-while loop. This post focuses on while loops in Java. In the video-lecture associated with this post, we compare side-by-side for loops and while loops.

While loops in Java

The while loop in Java has the following structure.

while (condition){
    //Code block
}

The variable condition must be a result of a boolean expression. That is, the variable condition is a boolean value (true/false). When the variable condition is true, the execution goes inside the code block. After executing the code block, the virtual machine (VM) comes back to the while condition to check if it is still true. If VM finds that the variable condition is still true, the execution goes inside the code block again.

VM keeps repeating the code block as long as the variable condition is true. If in any execution of the code block the value of the variable condition becomes false, then the VM does not go inside the next while-check. Hence the loop stops executing.

Problem Used in the Video

Print all the numbers between 1 and 10, separated by spaces. That is, the terminal output should look like the following one.

1 2 3 4 5 6 7 8 9 10

Of course, we are not going to hardcode ten numbers in a System.out.print statement. We will use a loop to print all the ten numbers. In the video, we will first use a for loop to print the ten numbers. Then, we will modify the for loop to a while loop. The output of the program will remain the same after the changes in the code.

The Solution

The solution using a for loop is provided below.

class WhileTest{
  public static void main(String[] args){
    int i;
    for (i=1;i<=10;i=i+1){
      System.out.print(i+" ");
    }
  }
}

The solution using a while loop is provided below.

class WhileTest{
  public static void main(String[] args){
    int i;
    i=1;
    while(i<=10){
      System.out.print(i+" ");
      i=i+1;
    }
  }
}

The Video Lecture

Here is the video lecture.

Transcription of the Audio of the Video

We are going to discuss another looping technique known as While-Loop. Everything we did using Java for-loops in the previous video lectures can be done using while-loops. Watch the video till the end for a detailed explanation on while-loops, a comparison between Java for-loops and while-loops, and a coding-example to explain how while-loops work.

While loop in Java

Hi, I am Dr. Monika Akbar. I am explaining Java while-loops today. A Java while-loop has this structure.

// Hand-draw

while (condition){
       // The code-block under the scope
}

In the while-loop structure, you have a “condition” to control the repetition of the loop. As long as this condition is true, the execution will keep going inside the while-loop and run the code-block again and again.

Inside the code-block, you can write something that will make the condition false after some number of iterations.

For loop in Java

Let us compare the while-loop structure with a for-loop structure. Let us quickly write the for-loop structure.

//Hand-draw

for (initialization; condition; change){      
// The code block under the scope
}

We have initialization, condition, and a change to control the for-loop. In the while-loop, we are missing the initialization, and the change. We have the condition part only. In an ideal looping, along-with the basic while-loop structure, we will need to include initialization and the change part, this way.

Initialization and change in a while loop

// Hand-draw

initialization;
while (condition){
     // The code block under the scope
     change;
}

Let us discuss this using an easy-to-solve example problem. Let us assume that the problem is to print all the numbers between 1 and 10 separated by spaces.

We are starting with a for loop

We can quickly write  a for-loop, in which we use an integer variable i to control the loop. In the initialization, i is equal to 1. The condition is that i  is smaller than or equal to 10. That means, as long as, the variable i remains within the range of 1 to 10, the loop will keep repeating. At the end of each iteration, i will increment by 1, as stated by the third part of the for-syntax.

We print the variable i inside the code. We put a space after i, so that on the terminal a gap is created between the current value of i and the next one.

Please save the file, compile it, and run the generated class file. All the integer numbers from 1 to 10 are printed on the terminal.

To make sure that there is no confusion, this part, containing “My Computer” is my command prompt. The text “My Computer” is not an outcome of the program we have written.

Now, we will use a while-loop instead of the for-loop to do the same task, that is printing the numbers from 1 to 10.

Difference between a for loop and a while loop in Java

Notice that there are some structural differences between a for loop and a while-loop. The basic while-loop only has the “condition” part for which the iteration will go inside. We will include the initialization part outside the while-loop, and the “change” part inside the code-block of while-loop.

Using while loop in Java

Let us keep the line that contains System.out.print  and delete the for structure.

Let us write the while statement. In parentheses we will write the condition for which the System.out.print statement will be executed. If the condition is true, everything inside the curly brackets will be executed.

For the initialization of i, let us write i=1 before the while statement.

After printing the current value of i, we do not want i to retain the same value because we want to print the next number in the next iteration. Therefore, we will change i to the next number. To do that we write i=i+1; right after where the current value of i is printed using the System.out.print statement.

Note that after this code segment executes, a number is printed and the value of i becomes one more than the number that was printed.

This line i=i+1 is responsible for the increment of i. Now, notice that the initialization is i=1. The loop will iterate and at the end of the iteration, the value of i will increase. We need to write a condition within the parentheses of the while-statement. The condition should be such that, the execution goes inside when the value of i is smaller than or equal to 10.

The condition is exactly the same one we had in the for-loop.

The output of the new program

This newly written code is an alternative of the code we wrote using a for-loop. The output of the code should be the same as before.

Let us save the file, compile the code, and execute the generated class file. Notice that we have exactly the same output, where we have all the 10 numbers starting from 1 and ending with 10. The numbers are separated by spaces.

Let us do a side by side comparison of the for-loop and the while-loop. The initialization of the for loop is a part of the structure of the for loop. In the while-loop, we wrote an initialization of the control-variable outside the while loop.

The condition is a part of the for-loop. The condition is a part of the basic while-loop too.

The increment operation is a part of the for-structure. The increment operation was not a part of the basic while-structure. However, we can incorporate the increment, or the change operation inside the code-block of the while loop.

In reality, the for-loop and the while loop can do the same thing.

Concluding remarks

We already learned nested for-loops in the previous video. Similar to nested for-loops, you can write nested while loops. You can even write one while-loop inside a for-loop, or even one for-loop inside a while-loop. The summary is, you can replace a for-loop by a while-loop and vice versa.

I hope the concept of while loop is clear to you. Please let us know if you have any question through the comment section below. If you haven’t subscribed to our website Computing4All.com and to the YouTube channel where this video is hosted, please do so to receive notifications on our new articles and video lectures. We wish you become successful in learning to code. Again, please do not hesitate to contact us via the comments section below, if you have any question. Or, even to introduce yourself. See you soon in another video.

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Nested looping refers to a loop inside another loop. Many applications require to loop over a repeated task. Nested looping is a solution to aid such repetitive tasks. As an example, consider printing ten lines on the terminal, where each line contains twenty asterisks, as shown below.

********************
********************
********************
********************
********************
********************
********************
********************
********************
********************

Printing one line of twenty asterisks can be performed using a loop. We can write ten lines of asterisks by running another loop over it ten times.

The Code used in the Video Lecture

In the video, we wrote a code using nested loops that prints the output of ten lines, where each line contains twenty asterisks. The java program is below. Please save the program in a file named Nested.java.

class Nested{
    public static void main(String[] args){
        int i;
        int j;
        for (i=1; i<=10;i=i+1){
            for (j=1;j<=20;j=j+1){
                System.out.print("*");
            }
            System.out.println();
        }
    }
}

The Video Lecture

The YouTube Video lecture is embedded below.

Exercise

Write a program using nested for loop to print the following pattern of asterisks on the terminal.

**********
*********
********
*******
******
*****
****
***
**
*

Transcription of the Audio of the Video

Hi,
This is Dr. Shahriar Hossain. How are you today? I hope that you are enjoying Java programming. In this video, I am going to explain nested loops. Nested looping refers to looping over another loop. Many applications rely on multiple levels of nesting. For simplicity, today we will learn how to use one for-loop inside another.

In this video, we will go over one problem. At the end of the video, we will provide an exercise. We will solve the exercise in the next video.

The problem

The problem we are going to solve is as follows: Print 10 lines, where each line contains 20 asterisks. The sample output is provided below.

[Show the sample output.]

********************
********************
********************
********************
********************
********************
********************
********************
********************
********************

[End of — Show the sample output.]

Analyzing the problem

Let us talk about the problem. Print 10 lines, where each line contains 20 asterisks, or stars, or multiplication symbols.

Let us think about the solution. Notice that we need to draw a line of 20 asterisks.

If we can draw one line that has 20 asterisks, we can repeat the process 10 times.

[Show the hand-written code]

Whatever code we will write should have this structure [as shown on screen.] The first thing is, we will try to print one line that contains 20 asterisks. That is, at first, we will solve this subproblem – print 20 asterisks in one line.

Printing one line of asterisks

Let us write our code in the main method in a class named Nested. Obviously, the name of the file is Nested.java.

Printing 20 asterisks can be done by typing writing System.out.println(“********************”);

Hard coding the asterisks will not make your code easy to change. That is, if someone wants to print fifty asterisks in one line, then you have to change the System.out.println with fifty asterisks.

Printing one line of asterisks using a for-loop

Anyway, we are going to use a loop that iterates over a System.out.print statement 20 times.

I am writing the structure of the for loop. As you can see, this for loop is designed to iterate 20 times. The value of the variable j will vary from 1 to 20 in this loop. Inside the for loop I use a System.out.print statement, which prints just one asterisk. Notice that this is a System.out.print statement not a System.out.println statement. That is, each asterisk will be printed one after another one, without any line.

Let us save the file, compile it, and run the generated class file. Twenty asterisks are printed on the terminal. Notice that my command line, which states “My computer” starts right after the last asterisk. I actually want to print all these 20 asterisks in a line. Nothing else should be here.

A new line

What we have to do is, we have to put a new line right after the last asterisk is printed.

Let us put a newline after the for loop ends. That is, after all the asterisks are printed, this System.out.println statement will print a new line. As a result, the text, “My Computer”, which is the prefix of my command prompt will move to the next line. Please notice again, System.out.println without any content in the parentheses simply prints a new line.

Let us save the file, compile it, and run the generated class file. All the 20 asterisks are now printed in one line. We have printed one line of twenty stars. That means we are done with this part. [Show the hand-written pseudocode.] We have to now implement this part, which is repetition of what we have done so far 10 times.

Repeating the previous loop

Now that we have the code to print just one line, we can repeat this part that prints one line of 20 stars, 10 times. If we repeat this part of the code 10 times, we should have the desired output, which is 10 lines, where each line has 20 asterisks.

To repeat this part 10 times, we need another for loop. To control that other for loop, we will need a variable. Let the variable be “i”. We write a for-loop, in which the variable “i” varies between 1 and 10. The code that prints 20 asterisks in a line is inside the outer for loop that iterates 10 times.

Running the program

Now save the java file, compile it, and run the generated class file.

Notice that all the 10 lines are printed. Each line contains 20 asterisks. Therefore, we have solved the problem. [Show the original problem]

Today, we have discussed the nested loops – one loop inside another one.

Nested looping can be more complex than what we have explained so far.

Exercise

We are providing an exercise now.

Print 10 lines, where the first line, contains 10 asterisks, the 2^nd line contains 9 asterisks, the 3^rd line contains 8 asterisks, the 4^th line contains 7 asterisks, so and so forth. The sample output is provided below.

**********
*********
********
*******
******
*****
****
***
**
*

We are giving this problem as an exercise. Please try to solve it before watching the next video.

Concluding remarks

It is fine if you cannot solve it at this point. We generally give exercises that are harder than what we have covered so far. That is what makes learners skilled. We will definitely provide the solution of the exercise and explain some relevant items in the next video.

If you have not yet subscribed to our website Computing4All.com and to this YouTube channel, please do so to confirm that you receive notifications on our new articles and videos. Wish you a wonderful day, evening, or night, whatever is upcoming. Thank you!

Repetition of segments of codes is an essential part of programming. Repeating the execution of a code segment, a programmer can reduce the size of the code as well as solve problems that require iterations of similar computations for an arbitrary number of times. Java provides three syntaxes for repetition: for loop, while loop, and do-while loop. This article covers Java for loop.

Java for loop

Java for loop is is a powerful syntax to repeat segments of code. It provides integral mechanisms to use variables to control a looping. The “for” syntax itself has three parts: initialization, condition, and change (modification of variables.) These parts are seperated by two semicolons. The basic for-structure is provided below.

for (initialization; condition; change){
// Write the code you need to repeat.
// This is the scope of the for loop.
}

The first part, initialization, is executed only once. It executes before anything else regarding the for-loop has been executed.

The second part, condition, executes each time the execution attempts to go insde the scope of a for-loop. The execution goes inside the loop if the condition results in true, otherwise it terminates the loop.

The third part, change, executes at the end of each iteration. Generally, increment or decrement operations on variables are applied in this part.

All the three parts are optional. Java for loop is a powerful syntax because a programmer can use it quite flexibly and creatively. In fact, knowing just “for loop” from the looping control statments is good enough. A programmer can skip while loop and do-while loop pretty easily, if she/he learns the for-loop well. (If you are reading this page for a coursework, I must tell you NOT TO SKIP while loop and do-while loop.)

The video lecture on Java for loop

The following video provides great details on how to use Java for loops. It is a great introductory material. The last part of the video contains a tracing of the program to visually explain how a Java for loop works.

The code used in the video lecture

Here is the code we used in the video lecture. Save the code in a file named MyCode.java.

class MyCode{
   public static void main(String[] args){
     int i;
     for (i=0; i<5; i=i+1){
       System.out.println("Hello Java!!!");
       System.out.println(i);      
     }
   }
 }

Exercise on Java for loop

Use Java for loop in solving all the problems below.

1. Write a program to print your name twenty times.
2. Write a program that sums up all the integers between 1 and 100 (including 1 and 100.) Report the final summation on the terminal.
3. Write a program that prints all the odd numbers between 0 and 50 on the terminal.

Comment

Please feel free to send us your code in solving the exercises above. Write your questions in the “Comments” section below. We will be happy to help you in problem-solving.

Transcription of the Audio of the Video

Hi, this is Dr. Shahriar Hossain. Have you ever thought about how can we repeat segments of our code for a certain number of times? Like most standard programming languages, Java has three different syntaxes  for repeating a segment of code. These syntaxes are called the “for loop”, the “while loop”, and the “do-while loop.”

Today, we are going to learn the “for loop.”

Sample problem

To explain a sample problem, let us write a program. The problem is to print “Hello Java!!!” five times. Based on topics we have discussed so far in this lecture series, we would write five System.out.println statements to print “Hello Java!!!” five times. If we have to write “Hello Java!!!” one hundred times, we have to write one hundred System.out.println statements. We might even have situations, where we have to repeat the same statement a thousand times. It is not quite practical to repeat statements so many times in the same program. To solve this issue, all languages provide looping.

Java for loop

Java’s “for” control statement has three parts. The first part is initialization. This part is executed once before entering the scope of the for loop. The second part is condition check. As long as this condition check is true, the execution will go inside the scope of the for loop. The third part is something that is automatically executed after each iteration of the scope.

All these three parts are separated by two semicolons, within the parentheses. Now notice that if you initialize a variable in the first part, and increase the variable in the last part, then you can put a condition in the second part to allow the execution to go inside certain number of times. For example, consider that you have a variable named “i”. You initialize the variable “i” to 0. Then you, say in the third part, i=i+1. The third part executes automatically after the execution of the segment scoped by the for loop. Therefore, at the end of each iteration i will automatically be incremented by 1.

You are starting the loop with i=0. After executing the code inside the scope of the for loop, the value of i will become 1 because i=i+1 will execute. In the next iteration, I will remain 1; then at the end of the iteration, i will become 2. This will continue for ever, unless you put a condition in the second part of the three parts of the for loop.

Terminating the loop

You can tell when to terminate the loop. In this example, you can tell “when to stop” based on the value of the variable i. Again, the second part should hold a condition; that is, it should result in a Boolean value. Before executing the scope, the program will check the second part if it is true. If it is not true, then the program will not go inside the loop.

If you type i<5, then it means as long as the value of “i” remains smaller than 5, the execution should go inside the scope of the for loop.

Summary of the three parts

Again, the first part is the initialization and executed only once. The third part is executed after every iteration. The second part is checked for “true” every time the execution attempts to go inside the scope of the for loop.

Since, we have i=0 in the first part, i<5 in the second part, and i=i+1 in the third part, this particular for loop will go inside the scope five times. We will discuss more on this soon in this video.

Let us use a Java for loop in our code

For now, let us change our code with five System.out.println statements so that our code contains only one System.out.println statement, but we repeat that statement five times using a for loop.

I am declaring an integer variable named “i”. I will use this integer variable to control the for loop.

Based on the discussion so far, all we have to do is, write a for loop, in which the first part will contain the initialization. I am putting i=0. In the second part I am putting i<5. In the third part I am writing i=i+1; Notice that, starting from 0, there are five integer numbers that are smaller than 5. Therefore, the loop will execute five times.

Let us save the file, compile, and run it. The program prints “Hello Java!!!” five times.

Values of “i” in each iteration

To check the value of the variable “i” during each of the five iterations, we can write another System.out.println statement, just to print the value of “i”. Save the file, compile, and run it.

Notice that after printing each of the “Hello Java!!!” phrases, we have a number printed in the next line which corresponds to the value of “i” in that particular iteration.

Let us trace the execution of the program.

Tracing the program

I am using a software to trace the program. You are already familiar with manual tracing from the previous video. In this video, I am doing tracing using a software named Netbeans to trace the execution of the code I have written. You do not have to use Netbeans at this point; I am using Netbeans because it gives a good visual illustration of what I am teaching today.

The light green highlight shows where the execution is right now.

I am going to track two items during this tracing. One is the value of the variable “i”  and the other is the Boolean value of “i<5”. I have the output-terminal too.

i=0

Now, the program is in a state where it has created memory space for the variable “i”. The execution is currently in the line where we have the syntax “for”. It has not yet executed the initialization i=0. The first thing the computer will do is execute, the initialization i=0. Then it will check if i<5. Because the variable “i” is zero after the initialization, 0<5 will be true. The execution will go inside the scope of the for loop. Notice that we have two System.out.println statements inside the scope of the for loop. The execution point is now on the first System.out.prinln statement.

At this point, the variable “i” is zero, as you can see here. Also notice that i<5 is true. This is the reason the “for” control statement has allowed the execution to go inside the scope of the for loop. If we execute the current line, which is System.out.println (“Hello Java !!!”), then “Hello Java !!!”  will be printed on the terminal. Our execution point has moved to the next line. Notice that “Hello Java !!!” has been printed on the terminal.

Again, the current value of the variable “i” is 0. Therefore, if we execute the current highlighted line, 0 will be printed on the terminal and here it is. 0 is printed on the terminal.

i=1

After 0 is printed on the terminal, the “for” control statement has executed the scope for the current iteration just once. Now, the third part of the for statement will execute. The third part is i=i+1. Again, the third part is executed at the end of each iteration. Once the variable “i” is incremented by 1, “i” becomes 1 because 0+1 is 1. At this point we are in the second iteration of the scope of the for loop. Notice that i<5 is a true statement because the variable “I” is 1, and 1 is smaller than 5 is a true statement. This is the reason why the execution was able to enter the scope with 1 as the value of i. We print “Hello Java!!!” for the second time on the terminal. Then we print the value of the variable “i”, which is 1 at this point.

i=2

Once the content of the variable “i” is printed on the terminal, i=i+1 will be executed and I will become 2. Since 2<5 is a true statement, the execution will go inside the scope. The first System.out.println will be executed. The execution will now go to the second System.out.println statement. Since the value of “i” is 2, the program will print 2. After printing 2, the third part of the for loop will be executed.

i=3

Therefore, the value of the variable “i” will become 3. Since 3<5 is a true statement, the execution will go inside the scope of the for loop. “Hello Java!!!” will be printed for the fourth time. The value of the variable “i”, which is 3 will be printed.

i=4

The value of the variable “i” will now become 4. Now, 4<5. Therefore, the execution will go inside the scope of the for loop. “Hello Java !!!” will be printed for the fifth time. In the next System.out.println statement 4 will be printed because the variable “i” now contains 4.

Our example loop terminates when i==5

At this point, the third part of the for syntax, which is i=i+1, will be executed. The variable “i” will become 5. Now 5<5 is a false statement. Therefore, the execution will not go inside the for loop anymore. Once the second part of the for loop becomes false, looping is terminated. The execution will jump what we have after the for loop. In our case, it is the closing curly bracket of the main method. Notice that, at this point the variable “i” is 5, and therefore the condition i<5 is false. This is the reason the for loop terminated.

By this time, we have printed “Hello Java!!!” five times on the terminal.

Now, won’t you be able to print “Hello Java!!!” ten times, on the terminal. Or say, print your name on the terminal fifty times, using a for loop? I’m sure you will.

Concluding remarks regarding Java for loops

Now that we can repeat code segments, we can write complicated codes. We can sum up all integers between 0 to 100. Or, we can find if a number is a prime number or not. Note that, you can write arbitrary number of lines inside the scope of the for loop. Those lines may contain anything including if-else if statements, or oven other for loops. More on this in the upcoming videos. If you have not already subscribed to our website Computing4All.com or to this YouTube channel, please do so to receive notifications on our new posts.

Thank you for watching the video. Hope to see you soon in in our video lecture series.

There are several control statements in Java, among which if-else if-else and switch statements are used for selection operations. The video lecture below explains if-else if-else statements. Programmers use if-else if-else statements for decision making in the code. That is, if-else if-else statements help in executing a part of the code based on certain conditions.

Prerequisites

Please make sure to go over the previous lecture on Boolean Variables and Relational Operators, if you haven’t already done so. The last lecture will give a good idea on Conditions, which is the basis for the current video.

The Video: if-else if-else statements in Java

The video explains if-else if-else statements in Java. It uses a simple example to explain the concept. Overall, the video will help beginners to start practicing if-else if-else statements.

The Program Used in the Video

The program demonstrated in the video is provided below. Please save the code in a file named ConditionTest.java if you want to use the code directly. We suggest that you type the code while you watch the video. When you type the code, you practically develope an understanding regarding the syntax you type.

import java.util.Scanner;
class ConditionTest{
    public static void main(String[] args){
        int x;
        int y;
        Scanner scan = new Scanner(System.in);
        System.out.println("Enter the 1st number");
        x=scan.nextInt();
        System.out.println("Enter the 2nd number");
        y=scan.nextInt();        
        if (x>y){
            System.out.println("x is greater");
        }else if (x<y){
            System.out.println("x is smaller");
        }else{
            System.out.println("Equal numbers");
        }
    }
}

Exercise to practice if-else if-else statements

Write a program that asks the user for a GPA on a scale of 0.0 to 4.0. If the user enters a number larger than 4.0 or less than 0.0, the program must output “Invalid GPA.” If the user enters a valid number, the program should display the corresponding letter grade based on the table below.

Please do not hesitate to send us your code via the comments section below. We will be happy to provide you feedback.

Comment

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Transcription of the Audio of the Video

From the previous video, you are familiar with comparisons and Boolean variables, we are now moving to what we can do with the comparisons. Practically, we can use comparisons for decision making in the program. That is, a part of our code will be executed if certain conditions are met; otherwise, another part of the code will be executed.

Starting of the code

I am starting my code where I will show how we can use if-else statements. The name of the class is ConditionTest; Of course the file name is ConditionTest.java. I have already written the main method, inside which I will write my code.

I am declaring two integer variables, x and y.

the variable scan is my Scanner object, using which I will get input from the user. I have written my code to get input for the first number x, and the second number y.

The first if statement

At this point, what I will do is, I will print a message if x and y have a certain relationship. The statement is written using “if” then in parentheses state the comparison. Within the parentheses, you must have a Boolean value. Notice that the comparison x>y results in a boolean value, either true or false.

Again, at first write if, then within parentheses provide the condition or comparison that results in a Boolean value. After the parentheses provide the scope of the code that should be executed if the condition in the parentheses results in “true”. You define the scope using a left curly bracket and a right curly bracket.

Anything you write inside the curly brackets will be executed, only if the condition you have provided within the “if” statement results in true. Inside the scope of the if statement I have written, I am writing a System.out.println statement. If x is greater than y, then the System.out.println will print “x is greater than y.”

Save, compile, and run

Let us save the file, compile it and run it. If the user enters a larger number for x than y, then the program should print “x is greater than y”, otherwise the program will print nothing after the user enters the numbers.

The user enters 10 for x and 5 for y. The program immediately prints “x is greater” because the first number the user provided is greater than the second number.

Let us run the code again. The user now provides 10 as the first number and 20 as the second number. Now, the program compares x>y, which results in the comparison 10>20, which in turn results in false. Since the if statement results in false, the System.out.println is not executed. The program just ends without printing anything.

Change the code to include another scope

Now, if we want the program to print something when x is not greater than y, then we can create another scope, which will be executed if the if statement results in false. What we write is, “else” and then we create another scope using left and right curly brackets.  You can print anything inside these curly brackets. Anything you print via a System.out.println statement will be printed on the terminal when x is NOT greater than y. Let us just print “x is not greater.”

Save, compile, and run the code

Let us save the file, compile it, and then run it.

Now, notice that for the first number 10, and the second number 20, the program outputs ” x is not greater.”

Earlier, the program was not printing anything for 10 and 20.

Running the program again with 20 and 10. Now the program is saying “x is greater.” That is if the first number if greater than the second number, the program says “x is greater”, otherwise the program says “x is not greater.”

What happens if you have two equal numbers

Now, what will happen if the user provides two equal numbers, say 10 and 10? Based on the code we have, the program will say that x is not greater. Notice that in the code, the if statement will result in false because x is not greater than y. Therefore, the first System.out.println will not be executed. The execution will go to the else part and execute the System.out.println of the scope of the else, which is “x is not greater.”

What if we want to say something different when x and y have the same value? Practically, we have to include a scope which will be executed when x is equal to y.

In the code, currently, we have if x is greater than y, then do something, otherwise, do another thing. The otherwise part executes only when x is smaller than or equal to y.

We will separate the smaller than part and the equal part. In the else part, we will include another if statement, with a condition x is smaller than y. When x is smaller than y, we want the program to print “x is smaller”.

Save this code, compile, and run the program. When the user puts 10 as the first number and 20 as the second number, the program outputs, “x is smaller.” It is the correct outcome.

When the user enters 20 as the first number and 10 is the second number, the program prints “x is greater.” This is a correct outcome too.

Now notice that when the user enters 10 as the first number and 10 as the second number, the program does not print anything. That is, when the user provides two equal numbers, the program does not go to any of the if scopes.

“The equal to” situation

We would like to see output for “the equal” situation too.

Notice that the first if statement handles the situation with x is greater than y. The second if statement, that is with else,handles the “x is smaller than y” situation. The only situation left is the “x is equal to y” situation. Therefore, we can simply add an “else” to handle the scope of “x is equal to y.” Inside the scope of “else”, we write “equal numbers,” within System.out.println.

We have now written a program that takes two numbers, x and y, from the user and gives an idea of which number is larger, or smaller, or if they are equal.

Let us save the file, compile the code, and run the program. Notice that for equal numbers, the program now outputs “Equal numbers.”

The general structure of if-else if-else statements

[Show the following on screen]

        if (condition 1) {
            ------------
        } else if (condition 2) {
            ------------
        } else if (condition 3) {
            ------------
        } 
            ------------
            ------------
        } else if (condition n) {
            ------------
        } else {
            ------------
        }

[End of — Show the following on screen]

Here is the general structure of “if then else” statements. The first “if” statement is straightforward. If more “if” statements are required in a sequence, they must be preceded by an “else”. You can write as many else if conditions as you need. You may end the if-then-else sequence with just an “else”. The last “else” will cover all situations that are not covered by all the if and else if statements you have in the sequence.

This overall sequence is called if-then-else statements. One thing I should mention is that, each scope under an “if” statement or an “else if” statement or an “else” statement may have many lines of code depending the problem the programmer is trying to solve. In our example, we just had a System.out.println statement within each scope.

Once a condition of the sequence is satisfied, the corresponding scope is executed. Nothing else will execute. The purpose of if-then-else sequence is to execute only one scope.

Conclusion

Please practice what we have discussed today. For exercises, please visit the link provided in the description. Subscribe to this YouTube channel and to our website Computing4All.com. We do not assume that you know anything about programming. Our video lectures, so far, are prepared for beginners regardless of background. Please start from the beginning of this lecture series if you are entirely a new learner.

Thank you very much for watching the video.