What is the function of final keyword in java

The functions of the final keyword in java are: 1. Modify references; 2. Modify methods; 3. Modify classes. When a method is final modified, this method will become the final method and cannot be overridden by subclasses. When final modifies a class, the class becomes the final class and cannot be inherited, such as the String class.

The final keyword can be used to modify references, methods and classes.

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1. Modified reference

If the reference is a basic data type, the reference is a constant. The value cannot be modified; if the reference is a reference data type, such as an object or array, the object or array itself can be modified, but the reference pointing to the address of the object or array cannot be modified; if the reference is a member variable of a class, it must be assigned a value on the spot , otherwise the compilation will report an error.

Code implementation:

final class Person {
    String name ="zs";    //3. 此处不赋值会报错
    //final int age;
    final int age = 10;  
}
public class Demo01 {
    public static void main(String[] args) {        //1. 基本数组类型为常量，无法修改
        final int i = 9;
        //i = 10;               //2. 地址不能修改，但是对象本身的属性可以修改
        Person p = new Person();
        p.name = "lisi";
        final int[] arr = {1,2,3,45};
        arr[3] = 999;
        //arr = new int[]{1,4,56,78};
    }
}

2. Modification method

When a final modification method is used, this method will become the final method and cannot be overridden by subclasses. However, the method can still be inherited.

class Person {
    public final void say() {
        System.out.println("说....");
    }
    public void eat() {
        System.out.println("吃...");
    }
}
class Teacher extends Person {
    //1. final修饰的方法不能被重写，但此方法仍然被继承
    /*@Override
    public void say() {
        System.out.println("老师在一本正经的说...");
    }*/
    
    public void eat() {
        System.out.println("老师在大口大口的吃...");
    }
}
public class Demo02 {
    public static void main(String[] args) {
        Teacher t = new Teacher();
        t.say();
    }    
}

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3. Used to modify the class

When a class is modified with final, the class becomes Final class, cannot be inherited. It is simply called "cutting off descendants and exterminating the descendants". For example, the String class is the final class.

Code implementation:

/***
 * final用法3：修饰类，则该类成为最终类，无法被继承
 * @author Administrator
 *
 */
final class Person02 {    }
//class Teacher02 extends Person02 { }
//class MyString extends String{}
public class Demo03 {

}

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