java中类的继承和访问控制

布满荆棘的人生 2022-04-06 08:55 167阅读 0赞

# 类的继承 #

TestPerson.java

class Person {
        private String name;
        private int age;
        public void setName(String name) {
        	this.name=name;
        }
        public void setAge(int age) {
        	this.age=age;
        }
        public String getName(){
        	return name;
        }
        public int getAge(){
        	return age;
        }
    }
    
    class Student extends Person {
        private String school;
        public String getSchool() {
        	return school;
        }
        public void setSchool(String school) {
        	this.school =school;
        } 
    }
    
    public class TestPerson {
        public static void main(String arg[]){
            Student student = new Student();
            student.setName("John");
            student.setAge(18);
            student.setSchool("SCH");
            System.out.println(student.getName());//John
            System.out.println(student.getAge());//18
            System.out.println(student.getSchool());//SCH
        }
    }

#  访问控制修饰符private protected public #

TestAccess.java

//对于class的权限修饰只可以用public和default
    public class TestAccess {
    }
    
    //权限控制
    class T {
    	//修饰符修饰成员变量
    	private int i = 0;//private	类内部
    	int j = 0;//default	类内部	同一包
    	protected int k = 0;//protected	类内部	同一包	子类
    	public int m = 0;//public	类内部	同一包	子类	任何地方
    	
    	public void m() {
    		i = 9;
    	}
    }
    
    class TT {
    	public void m() {
    		T t = new T();
    		//System.out.println(t.i);//TestAccess.java:18: 错误: i可以在T中访问private，不能访问private
    		System.out.println(t.j);//编译通过
    	}
    }