17 Java - Control Flow Statements

Chetan DattaChetan Datta
6 min read

Table of contents

Decision Making Statements

If then (Simple if)

  • If Condition is true, then if-block will get executed.
if(boolean condition){
    //Code here get executed when condition is true
}

if-else

  • If condition is true, if-block will get executed else if condition is false, then else-block will get executed.
if(boolean condition){
    //Code here get executed when condition is true
}
else{
    // Code here get executed when condition is false
}

if-else-if Ladder

It contains if-statements with multiple (chain of) else-if statements. It evaluate the condition from top and goes down and any condition gets true, its block will get executed.

public class Main {
    public static void main(String[] args) {
        int val = 13;

        if(val==1){
            System.out.println("val is 1");
        }
        else if (val == 2) {
            System.out.println("val is 2");
        }
        else if (val == 3) {
            System.out.println("val is 3");
        }
        else{
            System.out.println("val is: "+ val);
        }
    }
}

Nested-if statement

if-else statement within if-block or else-block

public class Main {
    public static void main(String[] args) {
        int val = 13;

        if(val>8){
            System.out.println("val is greater than 8");
            if (val<15){
                System.out.println("value is greater than 8 but less than 15");
            }
            else {
                System.out.println("value is greater than 15");
            }
        }
        else{
            System.out.println("val is less than 8 ");
        }
    }
}

Switch Statement

It is similar to if-else-if ladder, based on condition particular block will get executed based out of many alternatives.

Syntax

switch(expression){
    case value1:
        //code statments
        break;
    case value2:
        //code statments
        break;

    ...
    ...
    case valueN:
        //code statments
        break;
    default:
        //default code statements
        break;
}

Examples

Example 1:

public class Main {
    public static void main(String[] args) {
        int a = 1;
        int b =2;

        switch (a+b){
            case 1:
                System.out.println("a+b is 1");
                break;
            case 2:
                System.out.println("a+b is 2");
                break;
            case 3:
                System.out.println("a+b is 3");
                break;
            default:
                System.out.println(a+b);
                break;
        }
    }
}
/*
a+b is 3
*/

Example 2:

public class Main {
    public static void main(String[] args) {
        int a = 1;
        int b =2;

        switch (a+b){
            case 1:
                System.out.println("a+b is 1");
                break;
            case 2:
                System.out.println("a+b is 2");
                break;
            case 3:
                System.out.println("a+b is 3");
            case 4:
                System.out.println("a+b is 4");
            default:
                System.out.println(a+b);
        }
    }
}
/*
a+b is 3
a+b is 4
3
*/

Example 3:

public class Main {
    public static void main(String[] args) {
        int a = 1;
        int b = 2;

        switch (a+b){
            case 1:
                System.out.println("a+b is 1");
                break;
            default:
                System.out.println(a+b);
            case 2:
                System.out.println("a+b is 2");
                break;
        }
    }
}
/*
3
a+b is 2
*/

Example 4:

public class Main {
    public static void main(String[] args) {
        String month = "March";
        switch (month){
            case "January":
            case "February":
            case "March":
                System.out.println("month value is in Q1");
                break;
            case "April":
            case "May":
            case "June":
                System.out.println("month value is in Q2");
                break;
            default:
                System.out.println("month value is in Q3 or Q4");
        }
    }
}
/*
month value is in Q1
*/

Example 5: Same

public class Main {
    public static void main(String[] args) {
        String month = "March";
        switch (month){
            case "January","February","March":
                System.out.println("month value is in Q1");
                break;
            case "April","May","June":
                System.out.println("month value is in Q2");
                break;
            default:
                System.out.println("month value is in Q3 or Q4");
        }
    }
}
/*
month value is in Q1
*/

Few things we need to take care

  • Two cases cannot have the same value.

  • Switch expression data type and case values/constant data type should be same.

  • Case value should be either LITERAL or CONSTANT

Incorrect Usage

Correct Usage

public class Main {
    public static void main(String[] args) {
        final int value = 1;

        switch (2+1-2){
            case value:
                System.out.println("some code here");
            default:
                System.out.println("default code here");
        }
    }
}
/*
some code here
*/

All use cases need not to be handled

public class Main {
    public static void main(String[] args) {
        Day dayEnumVal = Day.FRIDAY;
        int outputValue = 0;

        switch (dayEnumVal){
            case MONDAY:
                outputValue = 1;
                break;
            case TUESDAY:
                outputValue = 2;
                break;
            case WEDNESDAY:
                outputValue = 3;
                break;
            case THURSDAY:
                outputValue = 4;
                break;
        }

        System.out.println(outputValue);
    }
}
/*
0
*/

Nested Switch statement is possible

public class Main {
    public static void main(String[] args) {
        Day dayEnumVal = Day.MONDAY;
        int outpuValue = 0;

        switch (dayEnumVal){
            case MONDAY:
                outputValue = 1;
                switch (outpuValue) {
                    case 1:
                        System.out.println("output val is 1");
                        break;
                    case 2:
                        System.out.println("output val is 2");
                        break;
                    default:
                        System.out.println("output val is "+ outpuValue);
                }

                break;
            case TUESDAY:
                outputValue = 2;
                break;
            case WEDNESDAY:
                outputValue = 3;
                break;
            case THURSDAY:
                outputValue = 4;
                break;
        }

        System.out.println(outputValue);

Supported Data Types

  • 4 Primitive types: int, short, byte, char

  • Wrapper Types of above primitive data types i.e. Integer, Short, Byte, Character.

  • Enum

  • String

Switch Expression

Return is not possible within Switch case.

There are 2 ways to do it:

  1. Using "case N ->" Label

  2. Using "yield" statement

Use of "case N ->"

public class Main {
    public static void main(String[] args) {

        String day = "";
        int val = 1;
        String outputVal = switch (val){
            case 1 -> "One";
            case 2 -> "Two";
            default -> "None";
        };
        System.out.println(day);
    }
}

All possible use cases need to be handled for the expression.

Using this "->" we can not have block of statements. If we want block statements and return the value, we need to use "yield"

Use of "yield"

public class Main {
    public static void main(String[] args) {

        String day = "";
        int val = 1;
        String outputVal = switch (val){
            case 1 -> {
                //some code logic here
                yield "One";
            }
            case 2 -> {
                //some code logic here
                yield "Two";
            }
            default -> "None";
        };
        System.out.println(day);
    }
}

Iterative Statements

for loop

Syntax

for(initialization of variable; condition check; increment/decrement of varaible){
    //statement block
}

public class Main {
    public static void main(String[] args) {
        for (int val=1; val<=5; val++){
            System.out.println(val);
        }
    }
}
/*
1
2
3
4
5
*/

Can also have a for loop inside a for loop

public class Main {
    public static void main(String[] args) {
        for (int x=1; x<=3; x++){
            for (int y=1; y<=3;y++){
                System.out.println("x="+x+" y="+y);
            }
        }
    }
}
/*
x=1 y=1
x=1 y=2
x=1 y=3
x=2 y=1
x=2 y=2
x=2 y=3
x=3 y=1
x=3 y=2
x=3 y=3
*/

while loop

initialize variable;
while(condition check){
    //block of statments
    increment/decrement variable
}

public class Main {
    public static void main(String[] args) {
        int val = 1;
        while (val<=5){
            System.out.println(val);
            val++;
        }
    }
}
/*
1
2
3
4
5
*/

do-while loop

initialize variable;
do{
    //block of statments
    increment/decrement variable
}while(condition check);

public class Main {
    public static void main(String[] args) {
        int val = 1;
        do{
            System.out.println(val);
            val++;
        }while (val<=5);
    }
}
/*
1
2
3
4
5
*/

for-each loop

public class Main {
    public static void main(String[] args) {
        int valArray[] = {1,2,3,4,5};

        for (int val: valArray){
            System.out.println(val);
        }
    }
}
/*
1
2
3
4
5
*/

Branching Statements

Break Statement

public class Main {
    public static void main(String[] args) {
        for (int val=1; val<=10; val++){
            if (val == 3){
                break;
            }
            System.out.println(val);
        }
    }
}
/*
1
2
*/

public class Main {
    public static void main(String[] args) {
        for (int outerLoop = 1; outerLoop<=5; outerLoop++){
            for (int innerLoop =1; innerLoop<=5; innerLoop++){
                if (innerLoop ==2){
                    break;
                }
                System.out.println(outerLoop+", "+innerLoop);
            }
        }
    }
}
/*
1, 1
2, 1
3, 1
4, 1
5, 1
*/

Continue Statement

public class Main {
    public static void main(String[] args) {
        for (int val=1; val<=10; val++){
            if (val == 3){
                continue;
            }
            System.out.println(val);
        }
    }
}
/*
1
2
4
5
6
7
8
9
10
*/
0
Subscribe to my newsletter

Read articles from Chetan Datta directly inside your inbox. Subscribe to the newsletter, and don't miss out.

Switch Expressioncontrol flowJavaSwitch casesoftware development

Written by

Chetan Datta
Chetan Datta

I'm someone deeply engrossed in the world of software developement, and I find joy in sharing my thoughts and insights on various topics. You can explore my exclusive content here, where I meticulously document all things tech-related that spark my curiosity. Stay connected for my latest discoveries and observations.