if...else

Java conditional statements if ... else

①if statement

An if statement contains a Boolean expression and one or multiple statements.

IF (Boolean expression) {
     // statement Boolean expression is true when it will be executed 
}

public class Test{
    public static void main(String args[]){
        int i=10;
        
        if(i<20){
            System.out.println("if语句");
        }
    }
}

operation result

The if statement

②if ... else statement

end of the statement may be followed if else statement, if statement when the boolean expression is false time, else statement blocks are executed

IF (Boolean expressions) {
     // Boolean expression is true, when executed 
} ELAS {
     // boolean expression is false when the execution 
}

public class Test{
    public static void main(String args[]){
        int i=50;

        if(i<20){
            System.out.println("if语句");
        }else{
            System.out.println("else语句");
        }
    }
}

operation result

else statement

③if ... else if ... else statement

if behind the statement may be followed by a lot else if ... else statement,

Note: if the statement at most one else statement, else statement following the else if all of the statements, if statements can have multiple else if statements; once one of the promising true Boolean expressions, and other statements skipped execution.

IF (Boolean expression 1 ) {
     // Boolean expression is true when performing 1 
} the else  IF (Boolean expression 2 ) {
     // Boolean expression is true when performing 2 
} the else  IF (Boolean expression 3 ) {
     // ...... 
} the else  IF (Boolean expression. 4 ) {
     // ...... 
} the else  IF (Boolean expression. 5 ) {
     // ...... 
} the else {
     // the above statement is not executed, this statement will be executed 
}

public class Test{
    public static void main(String args[]){
        int i=30;

        if(i==10){
            System.out.println("i为10");
        }else if(i==20){
            System.out.println("i为20");
        }else if(i==30){
            System.out.println("i为30");
        }else if(i==40){
            System.out.println("i为40");
        }the else { 
            System.out.println ( "I do not know what" ); 
        } 
    } 
}

operation result

i 30

④ nested if ... else statement

fi (Boolean expression 1) {
     // Boolean expression is true when performing an 
    IF (Boolean expression 2) {
         // boolean expression is true when performing 2 
    } 
}

public class Test{
    public static void main(String args[]){
        int i=10;
        int j=20;

        if(i<15){
            System.out.println("i比15小");
            if(j>15){
            　　System.out.println("j比15大");
            }
        }
    }
}

operation result

i less than 15 
big j than 15

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