Guide to Control Flow Statements in Java

Guide to Control Flow Statements in Java

Guide to Control Flow Statements in Java

Decision making is an important part of life. Many times you have to make decisions that will decide your next actions.

We do it in programming too.

Generally, the code executes from top to bottom. But sometimes you have to make some decisions that will decide which block of code executes first and which one later.

Control flow statements come to your help at that time.

Control flow statements let you control the flow of the execution of the code in your program. In Java programming language, you can control the flow of execution of the code by placing the decision making, branching, looping, and adding conditional blocks.

Based on this, we can classify the types of control flow statements as follows:

  1. Decision Making Statements
  2. Looping Statements
  3. Branching Statements
Control Flow Statements In Java

Control Flow Statements In Java

1. Decision Making Statements

We generally use decision-making statements when we have to decide which block of the code will be executed.

There are three types of decision-making statements.

  1. if statement
  2. if-else statement
  3. The switch statement

1. if statement

if statement is the most basic decision-making statement in the java programming language.

The syntax for the if statements is as given below:

There are two possible values of the condition, i.e. true and false.

The code block after the if statement will execute only if the value of the condition statement is true. If the value of the condition statement is false, the code block will not be executed.

Let’s see an example of the ‘if’ statement:

The output of the above program will be

We are getting this input because the condition statement number1<number2 evaluates to true hence the block of the code will be executed.

2. if-else statement

if-else statement is somewhat similar to the if statement, we are just adding an extra block of the code after the if statement.

If the value of the condition statement is true, the if block will be executed, else the else block will be executed.

Let’s see the syntax for if-else statement below:

Below, I have given an example of the if-else statement:

The out of the above program will be:

We are getting this output because the value of the condition statement number1<number2 is false hence the else block of code executed.

Nested if-else

In this type of if-else statement, we are nesting one if-else block in another if-else block. Either you can put your if-else block in the outer if block or else block.

Let’s see the syntax for a better understanding of the nested if-else statement. Here we are adding an extra if-else block in the outer if block.

In the above syntax, if the value of condition 1 is true, then only condition 2 will be checked. If the value of the condition 1 is false, then the outer else block will be executed.

Below, I have given an example of the nested if-else statement, as per the syntax shown above.

The output of the above program will be,

We are getting this input because condition 1 in the outer if statement is true hence the control enter in the outer if block and checks for condition 2.

Now the value of condition 2 is also true, so the ‘The number1 is less than 5.’ is printed as output.

As I said earlier, you can also put the if-else block in the outer else block. The syntax for the same is shown below:

If the value of condition 1 is true, then the outer if block will be executed.

If the value of condition 1 is false, the control goes in outer else block and condition 2 will be checked.

I have given below an example of the nested if-else statement as per the above syntax.

The output of the above program will be:

We are getting this input because the value of condition 1 is false hence the control enters in outer else block.

In the outer else block, the value of condition 2 is also false hence the inner else block executed.

3. The switch statement

We have seen the if-else statement above. If the condition is true, then only the if block will be executed, else the else block will be executed.

In the switch statement, there could be several execution paths.

I have given an example of the switch statement.

The output of the above program will be:

We are getting this input because the third case got executed. The break statement terminates the flow, and the rest of the conditions will not be checked. Finally, the last print statement got executed.

2. Looping Statements

We have seen all the decision-making statement, these statements make a decision and execute the block of the code based on that decision.

In looping statements, we are making a decision and executing the block of code multiple times. Until the condition is true, we are looping over the block of the code.

Each time we will check if the result of our decision statement is true or not, until and unless the result is true, we will execute the block of the code.

We can classify the lopping statements as follows:

  1. for loop
  2. while loop
  3. do-while loop

1. for loop

In the for loop, we are going to check the value of the condition statement. If the value is true, the block of the code will be executed.

After the successful execution of the code block, control again goes to the condition statement. Now, if the value is true, again the block of the code will be executed.

Also, we are declaring one variable which stores the number of iteration. Each time the for loop runs, the value of  i will be increased or decreased.

Below, I have given the syntax for the for loop.

In the above syntax, init is the variable initialization, the condition is the condition statement with its possible values true or false, and the last there is an increment or decrement operator, that will increment or decrements the variable.

I have given an example of the for loop below.

The output of the above program will be,

The above for loop will run until the value of i is less than or equal to 2. Once the value of i is greater than 2, i.e. at i=3, the for loop will not run.

Hence the for loop runs for 3 iterations i.e. 0. 1 and 2, and you can see the three print statements.

2. while loop

In a while loop, we do apply the initialization, condition statement and an increment or decrement operator like the for loop but the syntax is a little bit different.

The syntax of the while loop is given below.

We will see the same example for the while loop, that we have checked previously for the for loop.

The output of the above program will be:

In the first line of the code, we are initializing a variable i of integer type with the value 0.

In the next statement, we are checking the condition, if the value of the condition statement is true, the block of code will be executed.

When looking at the block of the code, at the end of the block you can see an increment operator, the value of i will increase by one, and the control goes to the condition statement. If the value of i is less than the 2, the block of code executes and so on.

When the value of the condition statement is false, the control goes to the next line of code after the while loop.

3. do-while loop

In the while loop, we are checking the condition statement first and then executing the block of code.

But in the do-while loop, we are first executing the block of code and then checking the condition.

If the value of the condition statement is true, the control goes at the starting of the code block, and the whole block of the code will be executed. Once the value of the condition statement is false, the control goes to the next line of code after the do-while loop.

I have given below the syntax for the do-while loop:

We will continue with the same example for the do-while loop:

The output of the above program will be:

In the above code, you can see that the for loop runs for 3 iterations i.e. 0. 1 and 2 hence you can see the three print statements.

The difference between the while and do-while loop is, in a while loop, we check the condition and executes the block of code, but in the do-while loop, we first execute the block of code and then check the condition.

You can see the below cartoon to understand the while and do-while loop.

An image showing the difference between the while and do while loop.

An image showing the difference between the while and do while loop. See original source.

Note: for-each loop

There is an updated version of the for loop called for-each loop.

We know to iterate over a collection with a simple for loop is really confusing, so Java introduces the for-each loop. We can use the for-each loop to iterate over the Arrays and Collections.

The syntax for the for-each loop is given below:

Also, I have given a simple example of the for-each loop below:

The output of the above program will be:

In the above program, we are iterating over an array, students. We have printed out the name of the array element i.e student using the for-each loop.

3. Branching Statements

Now we will see the branching statements. There are three types of the branching statements,

  1. break statement
  2. continue statement
  3. return statement

1. break statement

break statement terminates the control flow. Usually, we do use the break statement to terminate the flow of for, while and do-while loop.

I have given an example of the break statement below:

The output of the above program will be:

In the above example, the break statement will terminate the flow if the value of i will be equal to 4. Hence you can the statements up to statement index 3, i.e. 0, 1, 2, and 3.

Labeled break Statement

The simple break statement terminates the innermost for loop, but if you want to break the outer for a loop when the condition fulfills in the inner for loop, you can use the labeled break statement.

Below I have given an example of the labeled break statement with the for loop:

The output of the above program will be:

In the above example, we can see the break statement in the inner for loop with the search label. When condition fulfills .i.e when the j and i will be equal to 1, the break statement will terminate the flow of the inner for loop as well as the outer for loop.

This is happening just because we have placed the label search above the outer for loop. Hence the break statement is terminating the flow of both the for loop.

As per your requirement, you can place the label with the simple code block and mention that label with the break statement.

2. continue statement

continue statement skips the current iteration of the for, while and do-while loop. The simple continue statement skips the iteration of the innermost loop and sends the control back to the condition statement.

The code after the continue statement will not be executed for the current iteration.

Below I have given an example for the continue statement:

The output of the above program will be:

In the above example, we are trying to count the number of occurrences of the character ‘a’.

We are iterating over the intputString using the for loop.

In the for loop we have added a condition to check if the character at the current index is ‘a’ or not.

If the character at the current index is not ‘a’, we will execute the continue statement, which will skip the current iteration. If the character at the current iteration is ‘a’, then we will increase the count by one.

At last, we will get the number of times character ‘a’ comes in the inputString.

Labeled continue statement

We know the simple continue statement only skips the current iteration of the innermost loop. But when you have skipped the iteration of both inner loop as well as the outer loop, you can use the labeled continue statement.

The syntax for the labeled continue statement is similar to the labeled break statement.

3. The return statement

return statement can be found at the bottom line of the method.

The return statement exits from the current method and control flow return to the line from which the method was invoked.

You can write a return statement in the following ways:

The first return statement simply exits from the method, and the control flow goes to the line from which the method was invoked.

The second return the statement simply exits from the current method and returns the value of the variable. The control flow will go back to the line from which the method was invoked, and the returned value will be assigned to the variable at that line.

The third statement is similar to the second return statement, but instead of the variable, we are placing an expression. The expression will be evaluated before the exiting from the current method, and the result of the expression will be returned.

Below I have given an example of the return statement.

The output of the above program will be:

In the above example, I am returning the variable name of type string in the first method.

In the second method, I have written expression in the return statement. When control comes to the return statement, the expression got evaluated and the result i.e. 3 will be returned.

Conclusion

Controlling the flow of execution is one of the most important parts of the programming languages.

We have seen the control flow statements in the Java language.

In Java language, there are a total of three types of control flow statements. I have listed them below.

  1. Decision Making Statements
  2. Looping Statements
  3. Branching Statements

Decision-making statements can be classified as if, if-else, and switch statements.

Looping statements can be classified as for, while, and do-while loop.

Branching statements can be classified as break, continue, and return statement.

There is an enhanced version of the for loop, called a for-each loop. It came in Java 5. We can use the for-each loop to iterate over the Arrays and collections.

What is your experience while using the control flow statements? Please write down in the comment section below.

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6 comments

To-Ge January 29, 2020 at 12:09 pm
0

Bro you’re really using an image of Auschwitz for your Java Tutorial?

 
Marina Vorontsova January 29, 2020 at 12:38 pm
0

wait, is this Auschwitz? how do you know?

 
 
To-Ge January 29, 2020 at 2:49 pm
0

Referencing to his further photos on unsplash, i think it’s quite obvious: https://unsplash.com/@filippobonadiman

 
Gaurav Kukade January 29, 2020 at 1:38 pm
0

Hello brother, I am really sorry, I didn’t know the pic is from ‘Auschwitz’.

I chose this pic from Unsplash.com because of rails that show the analogy of the control flow statements.

Again, sorry!

 
 
To-Ge January 29, 2020 at 2:51 pm
0

No problem. I think these images were trending on unsplash, since it has been the 75th anniversary of the relief through the Red Army. Poor tagging from the photographer btw.

 
 
 
Marina Vorontsova January 30, 2020 at 3:27 pm
0

changed, mate, sorry it took so long.

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