4.3 Boolean Logical Operators_双语版Java程序设计-QQ阅读男生轻小说网

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4.3 Boolean Logical Operators

The boolean logical operators shown here operate only on boolean operands. All of the binary logical operators combine two boolean values to form a resultant boolean value. Table 4.3 lists logical operators.

Table 4.3 Logical Operators

class example4 {
    public static void main(String args[]) {
        boolean b;
        b = (2 > 3) && (3 < 2);
        System.out.println("b = "+b);
        b = false || true ;
        System.out.println("b = "+b);
    }
}

The output of the program is shown here:

b = false

b = true

Ternary Operator

Java includes a special ternary (three-way) operator that can replace certain types of if-then-else statement.

Java包含一个特殊的运算符(三元运算符)，可以替代语句if-then-else类型。

expression1 ? expression2 : expression3

Here, expression1 can be any expression that evaluates to a boolean value. If expression1 is true, then expression2 is evaluated; otherwise, expression3 is evaluated. The result of the ? operation is that of the expression evaluated. Both expression2 and expression3 are required to return the same type, which can’t be void.

先求解表达式1的布尔值，若为真则求解表达式2的值，否则求解表达式3的值。?运算的结果是被求解的表达式的值。要求表达式2和表达式3返回相同类型的值，这个值不能为空。

eg: int i=20;
    int j=30;
    int max = ( i > j ) ? x : j;

this section checks for the condition, if i is greater than j then value of i is assigned to max else value of j is assigned to max.

class example5 {
  public static void main(String args[]) {
      int i,k;
      i = 10;
      k = i < 0 ? -i : i;
      System.out.print("Absolute value of ");
      System.out.println(i + " is " + k);
      i = -10;
      k = i < 0 ? -i : i; //get absolute value of i
      System.out.print("Absolute value of ");
      System.out.println(i + " is " + k);
  }
}

when you run this program you will get following output:

Absolute value of 10 is 10

Absolute value of -10 is 10