java common keywords

： Commonly used keywords: 的 I. Access limited charters: It is the range of

access limited character used to modify class, attributes, methods, and constructive methods. Can be accessed

                                                                                                                                                         ‐ ’’’’’’’’’'''''‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐ accessible in the same class, in the same package, and in subclasses in different packages.            4. private Can only be accessed in the same class

2. this and super Usage of this:

This.Attribute This.Method(); Used to represent the current object

In the first line of the constructor method symbol, it indicates a certain constructor method of the current class                                                                                             ’ to ’ s ` ‐ ‐ ‐ ‐ L Cmp Pmp P P P P P P T S S P P P P S C P P S C P P S P C P P P S P P P P P S P P D P P S P M L M H D L E D Usage:

                                                                                                                                                                                                                    to be used in subclasses Represents the parent class object and calls the method of the parent class

                                                                                                                                                                                                                                                                              

 

This和super的使用代码 

public class Student {  
      
    public String name;  
      
    public Student(){  
        // this用在构造方法的第一行  
        // 表示当前类的某一个构造方法  
        this("张三");  
    }  
    public Student(String name){  
        this.name = name;     
    }  
    public void study(){  
        System.out.println(name+"在休息");  
    }

Java代码 

public class UNStudent extends Student{  
      
    public UNStudent(){  
        //默认调用父类的无参构造方法  
        super();  
        System.out.println("UNStudent");  
    }  
    public void study(){  
        System.out.println(name+"在学习");  
    }  
}

主类代码 

public class Main {  
    public static void main(String[] args) {  
          
                //创建Student类的对象  
        Student s = new Student();  
                //调用Student中的方法  
        s.study();  
          
                //创建UNStudent的对象  
        UNStudent u = new UNStudent();  
                //调用UNStudent中的方法  
        u.study();  
    }

  

 

       三、final

               final的用法：用来修饰类、变量、方法

               final修饰类： It means that this class cannot be inherited 不 Final modification method: It means that this method cannot be rewritten [coverage]

Final modifiers: indicate that this variable cannot be modified, and it can only be assigned once

🎜 🎜🎜 🎜🎜 🎜🎜 🎜🎜 🎜🎜 🎜🎜 🎜🎜 🎜🎜 🎜🎜 🎜🎜 🎜🎜 🎜🎜 🎜🎜 🎜🎜 🎜🎜 🎜🎜 🎜🎜 🎜🎜 🎜🎜 🎜🎜 🎜🎜 🎜🎜 🎜🎜 🎜🎜 🎜🎜 🎜🎜 🎜🎜 🎜🎜 🎜🎜 4. Usage: Can be used to modify classes, properties, methods, code blocks 🎜🎜                                                       .​ ​ ​ ​ static attribute [class attribute]: 🎜象 A attribute shared by all the objects of this category will only occupy a piece of memory space. 🎜🎜 Member attributes: 🎜🎜 Each object takes up a piece of memory separately, and must be called through the object to call 🎜🎜 STATIC method and members The difference between methods:                                                                                                                                                                                                                                         

                                         类方法中不能再调用this和super表示对象

                                         类方法是调用父类的还是子类重写的只和类名有关

 

                                成员方法：

                                        成员方法是调用父类的还是子类重写的只和对象本身有关

 

Java代码 

public class A {  
  
    public A() {  
        System.out.println("A");  
    }  
  
}

 

Java代码 

public class B {  
  
    public B() {  
        System.out.println("B");  
    }  
}

 

Static的使用代码 

public class Test {  
  
    //成员属性  
    public A a = new A();  
    //类属性  
    public static B b = new B();  
      
    //成员方法  
    public void change() {  
        System.out.println("change");  
    }  
      
    //类方法  
    public static void execute() {  
        System.out.println("execute");  
    }  
  
}

 

Java代码 

public class Demo {  
  
    public static void main(String[] args) {  
  
        //调用静态方法  
        Test.execute();  
  
        //调用成员方法需要对象  
        Test t = new Test();  
        t.change();  
          
          
    }  
  
}