29_instanceof关键字和类型转换

09_instanceof关键字和类型转换

1. instanceof用于判断对象和类的关系是否为父子

//Object>String
//Object>Person>Teacher
//Object>Person>Student
Object object = new Student();//引用object指向一个student对象
System.out.println(object instanceof Student);//true
System.out.println(object instanceof Person);//true
System.out.println(object instanceof Object);//true
System.out.println(object instanceof Teacher);//false
System.out.println(object instanceof String);//false
Person person = new Student();
System.out.println(person instanceof Student);//true
System.out.println(person instanceof Person);//true
System.out.println(person instanceof Object);//true
System.out.println(person instanceof Teacher);//false
//System.out.println(person instanceof String);//false
Student student = new Student();
System.out.println(student instanceof Student);//true
System.out.println(student instanceof Person);//true
System.out.println(student instanceof Object);//true
//System.out.println(student instanceof Teacher);//false
//System.out.println(student instanceof String);//false

2. 类型转换

//高<------------------低，Person类型被限制使用Student类方法
Person student = new Student();
//强制转换student对象为Student类型
Student student1 = (Student) student;
student1.eat();

public class Student extends Person{

    @Override
    public void run() {
        System.out.println("Student run");
    }
    public void eat(){
        System.out.println("Student eat");
    }
}

public class Person {
    public void run(){
        System.out.println("person run");
    }
}

小提示

1. 子类转换为父类，可能丢失自己的一些方法。
2. 子类转换为父类，向上转型，自动转换。
3. 父类转换成子类，向下转型，强制转换。