Java programming course: 5.6 Compound operators

In the previous lesson you learnt about logical operators and the if condition:

• Previous lesson: 5.5 Logical operators and the if condition
• Course contents 

Compound operators

If you need to test more than one condition at the same time you can use the logical and operator && or the logical or operator ||:

// Compound operators
int i = 3;
int j = 4;
double x = 8.4;
double y = 9.7;

// Logical and: both must be true
if ((i < j) && (x > y)) {
    // the first comparison is true and the second is false
    // therefore the final result is false and this block of
    // code will not be entered.
    System.out.println("Should not be output");
}

// Logical or: either (or both) must be true
if ((i < j) || (x > y)) {
    // the first comparison is true and the second is false
    // therefore the final result is true and this block of
    // code will be entered.
    System.out.println("Should be output");
}
 

Both above operators only make the second comparison if the first one does not preclude the final result. For example, in the first example above, had i not been less than j then the second comparison of x and y would not have taken place, since it would not affect the final outcome. Similarly, in the second example above, because i is less than j there is no need to test x and y.

Your condition expression may include several compound tests, and you can also include the ! symbol to negate the test:

// Using ! with compound comparisons
boolean sunny = true;
boolean raining = false;
boolean cold = false;
boolean windy = true;

if (sunny && !raining && !cold && windy) {
    System.out.println("It is sunny, not raining, " +
                       "not cold and is windy");
}
 

If you have methods that return a boolean these can also be used as the conditional expression:

private int temperature = 27;

public boolean isHot() {
    return (temperature >= 25);
}

public void weatherCheck() {
    if (isHot()) {
        System.out.println(“It is hot”);
    }
}
 

To negate a conditional for a method you can prefix the ! symbol:

if (! isHot()) {
    System.out.println(“It is not hot”);
}
 

In the next lesson you will learn about if...else... blocks.

Next lesson: 5.7 The If...else... block