java中类的继承和访问控制

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
    }
}