The difference between java constants and variables

The difference between Java constants and variables

1. Constants

Modify with final (also called final variable)

Constants must be assigned an initial value when declared, and the value cannot be modified after assignment

Constant names are usually expressed in all uppercase letters

You need to add the final or static final type modifier when declaring, for example:

private final int PI=3.141596; //常量，类加载时确定或者更靠后确定值
private static final int PI=3.14159;//静态常量（编译期常量），编译时就确定值（编译为class文件）

2. Variables

1. Different variable types, the allocated memory types are also different

2. Default value of uninitialized member variables

3. Automatic arithmetic operation conversion of variables

When performing arithmetic operations on two variables with different data types, the data needs to be processed first Type conversion

The system's automatic type conversion is performed from low to high precision

Automatic data type conversion rules:

Data conversion Example

//两个byte型数据相加
public class Add_two_byte{
  public static void main(String args[]){
    byte a = 5;
    byte b = 3;
    //byte c = a+b; 错误，两个操作数都转成int型
    int c = a+b; //正确操作
    System.out.println(a+"+"+b+"="+c);
  }
}

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