Java Data Types: Primitive and Reference Types Explained

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質問：

Introduce Java Data Types and give examples

回答：

Java is a statically typed programming language, which means that every variable must be declared with a data type before it can be used. Java has two main categories of data types: primitive data types and reference data types.

1. Primitive Data Types

Java has eight primitive data types, which are the building blocks of data manipulation in Java. They are:

  1. byte

    • Size: 8 bits
    • Range: -128 to 127
    • Example: 
      byte b = 100;

  2. short

    • Size: 16 bits
    • Range: -32,768 to 32,767
    • Example: 
      short s = 10000;

  3. int

    • Size: 32 bits
    • Range: -2^31 to 2^31-1
    • Example: 
      int i = 100000;

  4. long

    • Size: 64 bits
    • Range: -2^63 to 2^63-1
    • Example: 
      long l = 100000L; // 'L' suffix indicates a long literal

  5. float

    • Size: 32 bits
    • Range: Approximately ±3.40282347E+38 (6-7 decimal digits)
    • Example: 
      float f = 10.5f; // 'f' suffix indicates a float literal

  6. double

    • Size: 64 bits
    • Range: Approximately ±1.79769313486231570E+308 (15 decimal digits)
    • Example: 
      double d = 20.99;

  7. char

    • Size: 16 bits
    • Range: 0 to 65,535 (represents a single 16-bit Unicode character)
    • Example: 
      char c = 'A';

  8. boolean

    • Size: Not precisely defined (but typically 1 bit)
    • Values: true or false
    • Example: 
      boolean isJavaFun = true;

2. Reference Data Types

Reference data types are used to refer to objects and arrays. They do not store the actual data but rather a reference (or address) to the data. Some common reference data types include:

  1. String

    • Represents a sequence of characters.
    • Example: 
      String greeting = "Hello, World!";

  2. Arrays

    • A collection of elements of the same type.
    • Example: 
      int[] numbers = {1, 2, 3, 4, 5};

  3. Classes and Interfaces

    • User-defined data types that can encapsulate data and methods.
    • Example: 
      class Person {
    String name;
    int age;
}

Person person = new Person();
person.name = "Alice";
person.age = 30;

Summary

In summary, Java's data types can be categorized into primitive types, which are the basic building blocks, and reference types, which are used to create complex data structures. Understanding these data types is essential for effective programming in Java.

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