1.2 Variables and Data Types

1. Exam Points

• Data types
  • Primitive types: int, double, boolean
  • Reference types: String, any classes you define
• Output: statements to output information on the computer display:
  • System.out.println()
  • System.out.print()
• A literal (字面值) is the code representation of a fixed value.
  • 10, 2.3, true, ”anna”
• Declare an variable using the right data type.
  • int age = 10;
  • boolean isStudent = true;
  • double price = 2.3;

2. Knowledge Points

(1) Variables

• A variable is a storage location that holds a value, which can change while the program is running.
• Every variable has a name and an associated data type.
• Declare a variable(声明变量): type variableName
  • int x ;
  • double y , z ;
• Assign(赋值) a value to a variable:
  • x = 10 ;
  • y = 2.3 ;
• Declare a variable and initialize(初始化) the variable in the same statement:
  • int x = 10;
  • double y = 3.14 ;
  • String name = ”Annabelle” ;
• Note:
  • You must declare a variable before using it.
  • You must initialize a variable before using it.
  • You must not declare duplicate variables.

(2) Data Types

• A data type determines the values a variable can hold, and the operations on the variable.
• Data types can be categorized as:
  • Primitive type(原生类型): int, double, boolean.
    • int: int x = 10;
    • double: double y = 20.3
    • boolean(true or false): boolean isEven = true
  • Reference type(引用类型): any type other than the primitive types, such as String, Student, Dog, etc.
• In this course, we will only cover 3 primitive types: int, double, boolean.

3. Exercises

• Practice
• Solution