Operators and Assignments - Unary Operators

• operate on a single operand
• the unary ~ , + and - operators can only be applied to numeric primitive types
• the unary ! (logical complement) can only be applied to a boolean type
• rules of unary numeric promotion apply

• only used with integer values
• inverts the bits ie a 0-bit becomes 1-bit and vice versa
• in all cases ~x equals (-x)-1

    byte b0 = 7;             // binary: 0000 0111
    byte b1 = ~b0;           // binary: 1111 1000 ( -8 )
    
    ~7     = -7 -1       = -8
    ~3578  = -3578-1     = -3579
    ~-1234 = -(-1234)-1  =  1233

• returns the logical complement of a boolean type

    !(false) = true;    // complement of 'false' is 'true'
    !(true)  = false;   // complement of 'true' is 'false'

Unary + operator (JLS §15.15.3)

• the result of the unary + operator is a value not a variable

          byte b = +5;        // result: 5
  

The unary plus (+) operator has no effect on the sign of a value; it is included for symmetry only and to allow the declaration of constants
ie MIN_VALUE = +2.0; (JPL pg 128)

Unary - operator (JLS §15.15.4)

• for integers negation effect is the same as subtraction from zero
• two's complement is used for integers so for all values of x, -x equals (~x)+1

      
      byte b;
      b = -5;            // result: -5
      b = (~5) + 1;      // result: -5
      
  

• negation of the maximum negative int or long value results in the same number. An overflow occurs but no exception is thrown.

  int i;
  long l = 0L;
  i = -(-2147483648);          // result: -2147483648
  l = -(-9223372036854775808L) // result: -9223372036854775808;
  

• for floating-point negation is not the same as subtraction from zero
• the unary (-) operator merely negates the sign of the value

      double d = 0D;
      d = -(15.63);                   // result: -15.63
      d = -(-15.63);                  // result:  15.63
  

Example Code

• TestUnaryQuestions.java