2.5 Compound Boolean Expressions

1. Exam Points

• Use logic operators &&, || , !
• Precedence: ! > && > ||, left to right
• Short-circuit evaluation: a && b, a || b
• Note:
• For a method with a return type, a value must be returned (in all the cases).
• Left to right: in a>b && c>d, a>b is evaluated first

2. Knowledge Points

(1) Compound Boolean Expressions

• Commonly used operators in a boolean expression:
  • Relational operators: <, >, <=, >=, ==, !=
  • Logical operators: && (and), || (or), ! (not)
    • && : The expression a && b evaluates to true if both a and b are true and evaluates to false otherwise.
      
    • || : The expression a || b evaluates to false if both a and b are false.
    • ! : The expression !a evaluates to true if a is false and evaluates to false otherwise
      

(2) Precedence

• The order of precedence for evaluating logical operators is ! > && > ||.
  • Example 1:
    
    • In this example: && has a higher precedence over ||
  • Example 2:
    
    
    • In this example: first !, then &&, and then ||

(3) Short-circuit evaluation (短路评估/求值)

• Short-circuit evaluation (短路评估/求值) occurs when the result of a logical operation using && or || can be determined by evaluating only the first Boolean expression.
  • Example 1: &&
    
    
  • Example 2: ||
    

3. Exercises

• Practice
• Solution