Selection statements in Java

A selection statement is a control statements that allows the option between 2 or more execution paths in a program. Java supports 2 Types of selection statements i.e if and switch.

If statement in Java:
It is also called conditional branch statement

Simple if statement :
In simple if statement if a condition specified is satisfied then the if block will be executed. 

Syntax:
If (condition) { //sequence of statements }

Example:
public class SimpleIf { public static void main(String[] args) { int a=2; int b=5; if (a<b) { System.out.println(a+" "+"smaller than "+b); } } }

Output:

The if…else statement
In if…else statement if a condition specified is satisfied then the if block will be executed otherwise else block will be executed.

Syntax:
If (condition) { //sequence of statements } else { //sequence of statements }

Example:
public class SimpleIf { public static void main(String[] args) { int a=5; int b=2; if (a<b) { System.out.println(a+" "+"a is smaller than b "+b); } else { System.out.println(b+" "+" b is smaller than a "+a); } } }

Output:

 





Nested if…else statement
In nested if…else statement you can use one if or else if statement inside another else if statement

Syntax:
If(condition1) { If(condition2) { //Sequence of statements } Else { //sequence of statements } } Else { //sequence of statements }

Example:
public class GreaterNum { public static void main(String[] args) { int a=15; int b=25; int c=5; if(a>b) { if(a>c) { System.out.println("a is greater number"); } else { System.out.println("c is greater number"); } } else { if(c>b) { System.out.println("c is greater number"); } else { System.out.println("b is greater number"); } } } }

Output:

 




The if..else..if ladder
The sequence of nested if statement is called if..else…if ladder.

Syntax
if(condition) { //sequence of statements } else if(condition) { //sequence of statements; } else if(condition) { //sequence of statements; } ... else { //sequence of statements; }

Example:
public class IfElseIfLadder { public static void main(String[] args) { int month = 2; // Feb String season; if(month == 12 || month == 1 || month == 2) season = "Winter"; else if(month == 3 || month == 4 || month == 5) season = "Spring"; else if(month == 6 || month == 7 || month == 8) season = "Summer"; else if(month == 9 || month == 10 || month == 11) season = "Autumn"; else season = "Not a correct Month"; System.out.println("Feb is in the " + season + "."); } }

Output:

 




switch Statement:
The switch is the selection statement which is the multiway branch statement in java . We can say it is the best alternative for large series of if…else..if statement.

Syntax:
switch (expression) { case value1: // statement sequence break; case value2: // statement sequence break; ... case valueN: // statement sequence break; default: // default statement sequence }

Example:
public class SwitchStatement { public static void main(String[] args) { int a =3; switch(a) { case 0: System.out.println("a is zero."); break; case 1: System.out.println("a is one."); break; case 2: System.out.println("a is two."); break; case 3: System.out.println("a is three."); break; case 4: System.out.println("a is four."); break; default: System.out.println("a is greater than 3."); } } }

Output:

break statement is optional and if you omit , it will execute the next all case statements without checking the condition. 

If you omit the break statement from above Eg:
public class SwitchStatement { public static void main(String[] args) { int a =3; switch(a) { case 0: System.out.println("a is zero."); break; case 1: System.out.println("a is one."); break; case 2: System.out.println("a is two."); case 3: System.out.println("a is three."); case 4: System.out.println("a is four."); default: System.out.println("a is greater than 3."); } } }

The output will be as below even though a=3 ideally it should not.

 





Nested switch statement:
We can use the switch statement inside another switch statement.

Syntax:
switch (expression1) { case value1: switch(expression2) { case value1: //statements Break; Case value2: //Statements Break; Default: //Statements Break; } break; case value2: // statement sequence break; ... case valueN: // statement sequence break; default: // default statement sequence }

Difference between IF and Switch statement:
1) If statement is used to select among 2 alternatives . switch statement is used to select among multiple alternatives.
2) In if statement you compare about 2 objects using =,<,> but switch statement compares 2 objects only using equal.
3) If statement works under Boolean literal where as switch statement works under integer/character literals
4) Need to write complex code using if…else..if statement where as switch simplifies the complexity of the code .