JAVA switch case tutorial for beginners

JAVA switch case: Introduction

JAVA switch case statement is used, like the “if else” statement in making decision in our programs.

The JAVA switch case statement checks if a variable is equal to one value among a list of values.

The JAVA switch case statement works with a variable whose type is the following:

• byte
• char
• int primitive data types (int, long, short)
• enumerated types
• Wrapper Classes :  Character, Byte, Short, and Integer
• String (Java 7 supports also switch statements with Strings)

The syntax of the switch case statement is the following:

switch ( <expression> ) {

case <constant₁>:

<statement_or_block>*

[break;]

case <constant₂>:

<statement_or_block>*

[break;]

default:

<statement_or_block>*

[break;]

}

The switch statement works like this:

• <expression> is compared to each value of constant_i in order
• If <expression> is equal to constant_i, the “case constant_i” clause will be executed. Otherwise, the next case clause is checked.
• If <expression> is not equal to any constant_i, the default clause will be executed.
• The break keyword finishes the switch statement

Example:

This example displays the label of the month based on its number.

The month number 8 is August. So, the program displays August.

public static void main(String[] args) {
int month = 8;
switch (month) {
 case 1: 
System.out.println("January");           
break;

case 2: 
System.out.println("February");
break;
case 3: 
System.out.println("March");            
break;
case 4: 
System.out.println("April");
break;
case 5:  

System.out.println("May");

break;

case 6:  

System.out.println("June");

break;

case 7:  

System.out.println("July");

break;

case 8: 

System.out.println("August");           
break;
case 9: 
System.out.println("September");            
break;
case 10: 

System.out.println("October");
break;
case 11: 

System.out.println("November");
break;
case 12: 

System.out.println("December");
break;
default: 

System.out.println("Invalid month");
 break;

}

}
}

We can surely do the same thing using the “if else” statement. But, we will write much more lines of code.

Surely, this has a bad influence on the readability of our program.

public static void main(String[] args) {
int month = 8;
if (month == 1) {
System.out.println("January");
}
else if (month == 2){
System.out.println("February");
}
else if (month == 3){
 System.out.println("March");
}
else if (month == 4){
System.out.println("April");
}
else if (month == 5){
System.out.println("May");

}
else if (month == 6){

System.out.println("June");

}
else if (month == 7){
System.out.println("July");

}
else if (month == 8){
System.out.println("August");
}
else if (month == 9){
System.out.println("September");
}
else if (month == 10){
System.out.println("October");
}
else if (month == 11){
System.out.println("November");
}
else if (month == 12){

System.out.println("December");

}
else{
System.out.println("Invalid month");

}

}
}

JAVA switch case and the break keyword

The break keyword is necessary in order to make the switch case statement work properly.

In fact, when the program encounters the break keyword, it quits the switch statement and executes the instructions which come after the switch statement.

When we omit this keyword, we don’t get the expected result.

If we omit the break in the “case 1:” clause, the program still work as expected. But if we remove the break in the “case 8:” clause, we will get a bad behavior:

public static void main(String[] args) {
int month = 8;
switch (month) {
 case 1: 
System.out.println("January");      
break;
case 2: 
System.out.println("February");  
break;
case 3: 
System.out.println("March");
break;

case 4: 
System.out.println("April");
break;
case 5:  

System.out.println("May");
break;

case 6:  

System.out.println("June");
break;

case 7:  

System.out.println("July");
 break;

case 8: 
System.out.println("August");
case 9: 
System.out.println("September");
break;
case 10: 

System.out.println("October");
break;
case 11: 

System.out.println("November");        
break;
case 12: 

System.out.println("December");            
break;     
default: 

System.out.println("Invalid month");                    
break;
}
}
}

The output that we get from the program above is the following:

August

September

So, the “case 8:” was executed and the “case 9” also.

The break in the “case 9:” fished the switch statement.

If we remove the break keyword from all the “case” clauses after “case 9:” all the case clauses will be executed.

JAVA switch case VS JAVA if else statement:

The switch case statement offers better programs in term of readability. But, the case clause doesn’t support boolean expressions (equality, inequality, value in range, …).

In fact, the switch statement tests expressions based only on a single integer, enumerated value, or String object.

The if else statement supports these kind of conditions.