Java学习第十八节之instanceof和类型转换

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instanceof和类型转换

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instanceof

//Object > String//Object    Person>Teacher//Object    Person>StudentObject object = new Student();//System.out.println(X instanceof Y);//能不能编译通过！System.out.println(object instanceof Student);//trueSystem.out.println(object instanceof Person);//trueSystem.out.println(object instanceof Object);//trueSystem.out.println(object instanceof Teacher);//falseSystem.out.println(object instanceof String);//falseSystem.out.println("=================================");Person person = new Student();System.out.println(person instanceof Student);//trueSystem.out.println(person instanceof Person);//trueSystem.out.println(person instanceof Object);//trueSystem.out.println(person instanceof Teacher);//false//System.out.println(person instanceof String);//编译报错！System.out.println("=================================");Student student = new Student();System.out.println(student instanceof Student);//trueSystem.out.println(student instanceof Person);//trueSystem.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;import oop.demo06.Person;
import oop.demo06.Student;
import oop.demo06.Teacher;//一个项目应该只存一个main方法
public class Application {public static void main(String[] args) {//类型之间的转化：父  子//子类转换为父类，可能丢失自己的本来的一些方法Student student = new Student();student.go();Person person = student;}
}/*
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，减少重复的代码！简洁封装，继承，多态！   抽象类，接口*/