instanceof和类型转换
instanceof
package oop.demo01.demo06;
public class Person {
}
package oop.demo01.demo06;
public class Teacher {
}
package oop.demo01.demo06;
public class Student extends Person {
}
package oop.demo01.demo06;
public class Application {
public static void main(String[] args) {
//Object>Person>Student
Object object= new Student();
//System.out.println(x instanceof y);//能不能编译通过 即x与y是否存在关系
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
System.out.println("=============================================");
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);//编译报错
//System.out.println(person instanceof String);//编译报错
System.out.println("=============================================");
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);//编译报错
//System.out.println(student instanceof String);//编译报错
}
}
类型转换
package oop.demo01.demo06;
public class Person {
public void run(){
System.out.println("run");
}
}
package oop.demo01.demo06;
public class Teacher {
}
package oop.demo01.demo06;
public class Student extends Person {
public void go(){
System.out.println("go");
}
}
package oop.demo01.demo06;
public class Application {
public static void main(String[] args) {
//类型之间的转换：父 子
Person obj=new Student();
//student将这个对象转换为Student类型，我们就可以使用Student类型的方法了！
((Student) obj) .go();//类型转换
//子类转换为父类，可能丢失自己本来的方法
}
}
小结：
-
父类引用指向子类对象。
-
把子类对象转换为父类，向上转型。
-
把父类转换成子类，向下转型，强制转换。
-
方便方法的调用，减少重复的代码！