1.4 Assignment Statements and Input

1. Exam Points

• Assign a value to a variable based on its data type.
  • int x = 10;
  • double y = 2.3;
  • boolean z = true;
  • String name = "Annabelle";
• You’d better write clearly the value based on its type to avoid mistakes.
  • Ex. double a = 10/4; (a = 2.0)
  • Ex. int b = 10 / 2; (b = 5)

2. Knowledge Points

(1) Assignment Operator

• The assignment operator = is used to initialize or change the value stored in a variable.
  • int x = 10;
  • double y = 2.3;
  • String name = "Annabelle";
  • boolean isEven = false;
• Assign a proper value to each variable based on its data type.
• Note:
  • A variable must be assigned a value before being used.
  • Reference types can be assigned a new object or null if there is no object.
    • Dog d1 = new Dog(); // d1 refers to a newly created object
    • Dog d2 = null; // d2 refers to null, not refering to any object
  • null can not be assigned to a primitive data type variable.
• final variables: final variables can not be changed once initialized.
• The final keyword is used to declare a constant(常量) that can not be changed.

  int x = 10;
  // x is a variable, so its value can be changed
  x = 20; 
  
  // Y is a constant, its value can not be changed
  final int Y = 20; 
  
  // we normally use all uppercase to name a constant
  final int ERROR_CODE = 404; 
  

(2) Input

• Input can come in a variety of forms, such as tactile, audio, visual, or text.
• The Scanner class is one way to obtain text input from the keyboard.
• Since any specific form of input from the user is outside the scope of the AP CSA exam, so we will not talk about it in details.

3. Exercises

• Practice
• Solution