Java Notes (2) - Conditionals an

The note introduces how to use control flow and conditional statements in Java.

Java notes of open courses @Codecademy.

Boolean Operators

• &&: and operator

  • It returns a boolean value of true only when the expressions on both sides of && are true.

• ||: or operator

  • It returns a Boolean value of true when at least one expression on either side of || is true.

• !: not operator

  • It will return the opposite of the expression immediately after it. It will return false if the expression is true, and true if the expression is false.

• Boolean Operator Precedence

  • ! > && > ||
  • Every expression within parentheses is evaluated first.
  • Expressions are also read from left to right.

Conditional Expressions

• if statement

  • In Java, the keyword if is the first part of a conditional expression.
  • It is followed by a Boolean expression and then a block of code. If the Boolean expression evaluates to true, the block of code that follows will be run.
  • The if statement is not followed by a semicolon (;). Instead it uses curly braces ({ and }) to surround the code block.

• if/else statement

  • The if/else conditional will run the block of code associated with the if statement if its Boolean expression evaluates to true.
  • Otherwise, if the Boolean expression evaluates to false, it will run the block of code after the else keyword.

• if/elseif/else statement

  • If the Boolean expression after the if statement evaluates to true, it will run the code block that directly follows.
  • Otherwise, if the Boolean expression after the else if statement evaluates to true, the code block that directly follow will run.
  • Finally, if all previous Boolean expressions evaluate to false, the code within the else block will run.

• Ternary Conditional Statement

  • It can write if/else statements in a single line of code.
  • It from a Latin word that means "composed of three parts":
    • A Boolean expression
    • A single statement that gets executed if the Boolean expression is true
    • A single statement that gets executed if the Boolean expression is false
    • E.g., (Boolean expression) ? 'T' : 'F';

• Switch Statement

  • Java also provides a way to execute code blocks based on whether a block is equal to a specific value.

    int restaurantRating = 3;
    
    switch (restaurantRating) {
    
        case 1: System.out.println("This restaurant is not my favorite.");
          break;
    
        case 2: System.out.println("This restaurant is good.");
          break;
    
        case 3: System.out.println("This restaurant is fantastic!");
          break;
    
        default: System.out.println("I've never dined at this restaurant.");
          break;
    }
    

  • The break statement will exit the switch statement after a condition is met. Without the break statement, Java will continue to check whether the value of restaurantRating matches any other cases.

  • The default case is printed only if restaurantRating is not equal to an int with the value of 1, 2, or 3.

Review

• Boolean Operators: &&, ||, and ! are used to build Boolean expressions and have a defined order of operations
• Statements: if, if/else, and if/else if/else statements are used to conditionally execute blocks of code
• Ternary Conditional: a shortened version of an if/else statement that returns a value based on the value of a Boolean expression
• Switch: allows us to check equality of a variable or expression with a value that does not need to be a Boolean

External Resources

• More Java Operators
• Control Flow Statements