Decision and control statements

In Java, decision and control statements allow you to select and execute specific blocks of the code while skipping other sections or statements.

The if statement

The if statement consists of a condition followed by one or more statements.

The syntax of an if statement is as follows:

if(condition) 
{ 
    //Statements will execute if the condition is true 
}

An example of this is as follows:

package MyFirstPackage;
  public class IfCondition {
  public static void main(String[] args) {
    int empSal = 20000;
    if (empSal >= 10000) {
      System.out.println("he is a manager...!");
    }
    else 
    {
      System.out.println("he is NOT a manager...!");
    }
  }
}

The output of the preceding code is as follows:

he is a manager...!

The if...else statement

The if statement can be followed by an optional else statement, which executes when the condition is false.

The syntax of an if...else statement is:

if(condition){ 
    //Executes when the condition is true 
}else{ 
    //Executes when the condition is false 
}

The if...else if...else statement

The if statement can be followed by an optional else if...else statement, which is very useful to test various conditions using single if...else if statement.

The syntax of an if...else statement is:

if(condition 1){ 
  //Executes when the condition 1 is true 
}else if(condition 2){ 
  //Executes when the condition 2 is true 
}else if(condition 3){ 
  //Executes when the condition 3 is true 
}else { 
  //Executes when the one of the above condition is true. 
} 

The nested if...else statement

It is always legal to nest if..else statements. When using if...else if... else... statements, there are a few points to keep in mind:

• An if statement can have zero or one else statement and it must come after any else if statements

• An if statement can have zero to many else if statements and they must come before the else statement

• Once an else if statement succeeds, none of the remaining else if statements or else statements will be tested

The syntax for a nested if...else statement is as follows:

if(condition 1){ 
  //Executes when the condition 1 is true 
  if(condition 2){ 
    //Executes when the condition 2 is true 
  }
}

The switch statement

A switch statement allows a variable to be tested for equality against a list of values. Each value is called a case, and the variable being switched on is checked for each case.

The syntax of a switch statement is:

switch(expression){ 
case value : 
//Statements 
break; //optional 
case value : 
//Statements 
break; //optional 
//You can have any number of case statements. 
default : //Optional 
//Statements 
}