instanceof和类型转换

instanceof和类型转换

instanceof判断具体实例与类对象的关系

package Demo01;public class Person {}

package Demo01;public class Student extends Person{}

package Demo01;public class Application {public static void main(String[] args) {//Object->String//Object->Person->StudentObject student = new Student();System.out.println(student instanceof Student);System.out.println(student instanceof Person);System.out.println(student instanceof Object);System.out.println(student instanceof String);System.out.println( );Student student1 = new Student();System.out.println(student1 instanceof Student);System.out.println(student1 instanceof Person);System.out.println(student1 instanceof Object);//System.out.println(student1 instanceof String);System.out.println( );Person student2 = new Student();System.out.println(student2 instanceof Student);System.out.println(student2 instanceof Person);System.out.println(student2 instanceof Object);//System.out.println(student2 instanceof String);//System.out.println(x instanceof Y);判断x和Y有没有继承关系//具体实例与实际类型的父子类的instanceof为true//具体实例与引用类型的父子类的instanceof为false}
}

输出结果为：

true
true
true
false

true
true
true

true
true
true

---

类型转换

1. 父类引用指向子类的对象
2. 把子类转换为父类，向上转型
3. 把父类转换为子类，向下转型；强制转换
4. 方便方法的调用，减少代码的重复性，更简洁。

package Demo01;public class Person {}

package Demo01;public class Student extends Person{
public void test(){System.out.println("测试");
}}

package Demo01;public class Application {public static void main(String[] args) {//Student为Object的子类 由低转高Object a = new Student();//a.test()无法使用Student的方法因为不是Student类型//将a对象转换成Student类型，使用其方法Student a1 = (Student) a;a1.test();Student student1 = new Student();Person person=student1;//person.test();//子类转成父类，会丢失原本自己子类的方法}
}

输出结果为：

测试