1.final is a keyword in the Java language
2.final means final, immutable
3.final modified class cannot be inherited
4.final modified method cannot be overwritten
5.final modified variable: can only be assigned once value
//final修饰类
final class A{
}
class B extends A{
}
//final修饰方法
class C{
public final void doSome(){
System.out.println("C doSome");
}
}
class D extends C{
public void doSome(){
System.out.println("D doSome");
}
}
public class Test{
public static void main(String[] args){
B b = new B();
D d = new D();
d.doSome();
//final 修饰局部变量
final int i;
i = 10;
final int j = 100;
j = 300;
}
}
6. For references, after the final modified reference points to object A, it can no longer point to object B, but the data inside object A can be modified.
7. The final modified instance variable must be manually assigned (meaning of manual assignment: assignment after variable, assignment by constructor)
- If the instance variable is not manually assigned, the system will assign a default value
- And final modified variables: can only be assigned a value
- Therefore, the final modified instance variable, regardless of the default value assigned by the system, requires the programmer to manually assign the value
- Obviously Java designers are reluctant to bear this pot.
- Manual assignment: There are two ways to write directly and construct in the syntax, but they are all assigned when the object is created
class User{
//final修饰实例变量
//会报错，没有为age赋值
//final int age;
final double height = 1.8;
final double weight;
//在构造方法中为finalx修饰的实例变量赋值会报错吗？
public User(){
weight = 90;
}
}
Review: Instance variables are assigned when the object is created.
So both height and weight are assigned initial values when a User object is created
8.final modified instance variable means that this variable will not change with the change of the object,
so conclusion: final modified instance variable, generally add static declaration as static variable to save memory.
Ultimate conclusion: static final joint declared variable is called " "Constant", constant names are recommended to be capitalized, and each word is underlined
class Chinese{
String id;
String name;
static final String COUNTRY = "中国";
}