深入理解JAVA继承
特性
继承是将父类对象包含在子类对象中,父类对象中所有的一切皆在子类对象中父类private字段和方法只是对子类不可见,实际仍旧是存在的在子类中声明与父类同名的字段时,例name,此时子类中包含两个name字段:this.name,super.name当不重写父类方法时,调用的就是父类对象的方法,其实操作的就是父类对象若重写父类方法,根据Java多态的特性,调用的是子类重写方法,父类方法只有通过super指针调用多态只对方法起作用,不对字段起作用
举例
实例1
//父类对象
public class Person {
private String name;
public String getName() {
return name;
}
public void setName(String name) {
this.name = name;
}
}
//子类对象
public class Teacher extends Person{}
public class Solution {
public static void main(String[] args) {
Teacher teacher = new Teacher();
teacher.setName("zhangsan");
System.out.println(teacher.getName());
}
}
//输出
zhangsan
结论
子类对象包含父类对象private字段(debug查看内存可以查看到name字段)private字段对子类不可见(即this指针无法访问到)不重写父类方法时,调用的是父类对象的get/set方法可通过父类的get/set方法访问到父类对象的private字段
实例2
//父类对象
public class Person {
private String name;
public String getName() {
return name;
}
public void setName(String name) {
this.name = name;
}
}
//子类对象
public class Teacher extends Person{
private String name;
public String getName() {
return name;
}
@Override
public String toString() {
return "Teacher.name = " + this.getName() + " Person.name = " + super.getName();
}
}
public class Solution {
public static void main(String[] args) {
Person teacher = new Teacher();
teacher.setName("zhangsan");
System.out.println(teacher.getName());
System.out.println(teacher.toString());
}
}
//输出
null
Teacher.name = null Person.name = zhangsan
结论
当在子类中声明与父类同名字段时,对象中包含两个name（debug查看内存可查看到）此时可分为this.name和super.name两个字段未重写set方法,故调用的时父类对象的set方法,对父类对象的name赋值重写了get方法,根据Java多态特性,调用子类对象的get方法
实例3
//父类对象
public class Person {
private String name;
public int age = 38;
public String getName() {
return name;
}
public void setName(String name) {
this.name = name;
}
}
//子类对象
public class Teacher extends Person{
private String name;
public int age = 26;
public String getName() {
return name;
}
@Override
public String toString() {
return "Teacher.name = " + this.getName() + " Person.name = " + super.getName();
}
}
public class Solution {
public static void main(String[] args) {
Teacher teacher = new Teacher();
Person person = teacher;
teacher.setName("zhangsan");
System.out.println(teacher.getName());
System.out.println(teacher.toString());
System.out.println(teacher.age);
System.out.println(person.age);
}
}
//输出
null
Teacher.name = null Person.name = zhangsan
26
38
结论
当在子类中声明与父类同名字段时,对象中包含两个name（debug查看内存可查看到）此时可分为this.name和super.name两个字段方法存在多态特性,字段不存在多态特性
