Control Statements in Java

Introduction

A program executes from top to bottom, except when we use control statements. Then, we can control the order of execution of the program, based on logic and the values.

In Java, control statements can be divided into the following three categories:

Selection Statements
Iteration Statements
Jump Statements

Selection Statements

Selection statements allow you to control the flow of program execution, on the basis of the outcome of an expression or state of a variable, known during runtime.

Selection statements can be divided into the following categories:

The if and if-else statements
The if-else statements
The if-else-if statements
The switch statements

The if statements

The first contained statement (that can be a block) of an if statement, only executes when the specified condition is true. If the condition is false and there is no keyword, then the first contained statement will be skipped and execution continues with the rest of the program. The condition is an expression that returns a boolean value.

Example

package com.deepak.main;
import java.util.Scanner;
public class IfDemo {
public static void main(String[] args) {
int age;
Scanner inputDevice = new Scanner(System.in);
System.out.print("Please enter Age: ");
age = inputDevice.nextInt();
if (age > 18)
System.out.println("above 18 ");
}
}

Output

The if-else statements

In if-else statements, if the specified condition in the if the statement is false, then the statement after the else keyword (that can be a block) will execute.

Example

package com.deepak.main;
import java.util.Scanner;
public class IfElseDemo {
public static void main(String[] args) {
int age;
Scanner inputDevice = new Scanner(System.in);
System.out.print("Please enter Age: ");
age = inputDevice.nextInt();
if (age >= 18)
System.out.println("above 18 ");
else
System.out.println("below 18");
}
}

Output

The if-else-if statements

The statement following the else keyword can be another if or if-else statement.

That would look like this:

if (condition)
statements;
else if (condition)
statements;
else if (condition)
statement;
else
statements;

Whenever the condition is true, the associated statement will be executed and the remaining conditions will be bypassed. If none of the conditions are true, then the else block will execute.

Example

package com.deepak.main;
import java.util.Scanner;
public class IfElseIfDemo {
public static void main(String[] args) {
int age;
Scanner inputDevice = new Scanner(System.in);
System.out.print("Please enter Age: ");
age = inputDevice.nextInt();
if (age >= 18 && age <= 35)
System.out.println("between 18-35 ");
else if (age > 35 && age <= 60)
System.out.println("between 36-60");
else
System.out.println("not matched");
}
}

Output

The Switch Statements

The switch statement is a multi-way branch statement. The switch statement of Java is another selection statement that defines multiple paths of execution, of a program. It provides a better alternative than a large series of if-else-if statements.

Example

package com.deepak.main;
import java.util.Scanner;
public class SwitchDemo {
public static void main(String[] args) {
int age;
Scanner inputDevice = new Scanner(System.in);
System.out.print("Please enter Age: ");
age = inputDevice.nextInt();
switch (age) {
case 18:
System.out.println("age 18");
break;
case 19:
System.out.println("age 19");
break;
default:
System.out.println("not matched");
break;
}
}
}

Output

An expression must be of a type of byte, short, int, or char. Each of the values specified in the case statement must be of a type compatible with the expression. Duplicate case values are not allowed. The break statement is used inside the switch to terminate a statement sequence. The break statement is optional in the switch statement.

Iteration Statements

Repeating the same code fragment several times, until a specified condition is satisfied, is called iteration. Iteration statements execute the same set of instructions, until a termination condition is met.

Java provides the following loop for iteration statements:

The while loop
The for loop
The do-while loop
The for-each loop

The while loop

It continually executes a statement (that is usually a block) while a condition is true. The condition must return a boolean value.

Example

package com.deepak.main;
public class WhileDemo {
public static void main(String[] args) {
int i = 0;
while (i < 5) {
System.out.println("Value :: " + i);
i++;
}
}
}

Output

The do-while loop

The only difference between a while and a do-while loop, is that do-while evaluates its expression at the bottom of the loop, instead of the top. The do-while loop executes at least one time, then it will check the expression prior to the next iteration.

Example

package com.deepak.main;
public class DoWhileDemo {
public static void main(String[] args) {
int i = 0;
do {
System.out.println("value :: " + i);
i++;
}
while (i < 5);
}
}

Output

The for loop

A for loop executes a statement (that is usually a block) as long as the boolean condition evaluates to true. A for loop is a combination of the three elements initialization statement, boolean expression and increment or decrement statement.

Syntax:

for ( < initialization > ; < condition > ; < increment or decrement statement > ) {
< block of code >
}

The initialization block executes first before the loop starts. It is used to initialize the loop variable.

The condition statement evaluates every time prior to when the statement (that is usually a block) executes. If the condition is true then only the statement (that is usually a block) will execute.

The increment or decrement statement executes every time, after the statement (that is usually a block).

Example

package com.deepak.main;
public class WhileDemo {
public static void main(String[] args) {
int i = 0;
while (i < 5) {
System.out.println("Value :: " + i);
i++;
}
}
}

Output

For each loop

This was introduced in Java 5. This loop is basically used to traverse the array or collection elements.

Example

package com.deepak.main;
public class ForEachDemo {
public static void main(String[] args) {
int[] i = {
1,
2,
3,
4,
5
};
for (int j: i) {
System.out.println("value :: " + j);
}
}
}

Output

Jump Statements

Jump statements are used to unconditionally transfer the program control to another part of the program.

Java provides the following jump statements:

break statement
continue statement
return statement

Break Statement

The break statement immediately quits the current iteration and goes to the first statement, following the loop. Another form of break is used in the switch statement.

The break statement has the following two forms:

Labelled Break Statement
Unlabeled Break Statement

Unlabeled Break Statement: This is used to jump program control out of the specific loop on the specific condition.

Example

package com.deepak.main;
public class UnLabeledBreakDemo {
public static void main(String[] args) {
for (int
var = 0;
var < 5;
var ++) {
System.out.println("Var is : " +
var);
if (var == 3)
break;
}
}
}

Output

Labelled Break Statement

This is used for when we want to jump the program control out of nesting loops or multiple loops.

Example

package com.deepak.main;
public class LabeledBreakDemo {
public static void main(String[] args) {
Outer: for (int var1 = 0; var1 < 5; var1++) {
for (int var2 = 1; var2 < 5; var2++) {
System.out.println("var1:" + var1 + ", var2:" + var2);
if (var1 == 3)
break Outer;
}
}
}
}

Output

Continue Statement

The continue statement is used when you want to continue running the loop, with the next iteration, and want to skip the rest of the statements of the body, for the current iteration.

The continue statement has the following two forms:

Labelled Continue Statement
Unlabeled Continue Statement

Unlabeled Continue Statement

This statement skips the current iteration of the innermost for, while and do-while loop.

Example

package com.deepak.main;
public class UnlabeledContinueDemo {
public static void main(String[] args) {
for (int var1 = 0; var1 < 4; var1++) {
for (int var2 = 0; var2 < 4; var2++) {
if (var2 == 2)
continue;
System.out.println("var1:" + var1 + ", var2:" + var2);
}
}
}
}

Output

Labeled Continue Statement

This statement skips the current iteration of the loop with the specified label.

Example

package com.deepak.main;
public class LabeledContinueDemo {
public static void main(String[] args) {
Outer: for (int var1 = 0; var1 < 5; var1++) {
for (int var2 = 0; var2 < 5; var2++) {
if (var2 == 2)
continue Outer;
System.out.println("var1:" + var1 + ", var2:" + var2);
}
}
}
}

Output

Return Statement

The return statement is used to immediately quit the current method and return to the calling method. It is mandatory to use a return statement for non-void methods to return a value.

Example

package com.deepak.main;
public class ReturnDemo {
public static void main(String[] args) {
ReturnDemo returnDemo = new ReturnDemo();
System.out.println("No : " + returnDemo.returnCall());
}
int returnCall() {
return 5;
}
}

Output