Week 6

Conditionals

You Will Understand Why We Need Conditions

• To make decisions based off different inputs.
• Perform different actions in the same program.

Basics

• if, switch, else if
• boolean expression, boolean variable, boolean method call
• executes or bypasses statements in block

  if (x > 0) {
      System.out.println("x is positive");
  } else if(x == 0) {
      System.out.println("x is 0");
  } else {
      if( x > -10 ) {
          System.out.println("x is negative, but barely");
      }
      System.out.println("x is negative");
  }
  

Relational operators OR Comparison Operators

    x == y // x is equal to y
    x != y // x is not equal to y
    x > y  // x is greater than y
    x < y  // x is less than y
    x >= y // x is greater than or equal to y
    x <= y // x is less than or equal to y
    // Strings are different because they are special/immutable objects
    aStr.equals("abc");

Logical operators

    &&  Logical and Returns true if both statements are true    x < 5 &&  x < 10    
    ||  Logical or  Returns true if one of the statements is true   x < 5 || x < 4  
    !   Logical not Reverse the result, returns false if the result is true !(x < 5 && x < 10)

Short Circuit Evaluation

• The first condition that satisfies the condition stops evaluation

DeMorgan’s Law

    !(A && B) isthesameas !A || !B
    !(A || B) isthesameas !A && !B

Recursion is Important

• But we’re not going to cover that much in this class

Review

• Modulus
• Variables in methods
• Why we use methods
• class/static vs public/object/instance