instanceof

public class Person {public void run(){System.out.println("run");} } public class Student extends Person{ } public class Teacher extends Person{ } public class Application {public static void main(String[] args) {// instanceof 是 Java 的保留關(guān)鍵字。它的作用是測試它左邊的對象是否是它右邊的類的實例，返回 boolean 的數(shù)據(jù)類型。// Object > String// Object > Person > Teacher// Object > Person > StudentObject object = new Student();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); // 編譯報錯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); // 編譯報錯 // System.out.println(student instanceof String); // 編譯報錯}}

類型轉(zhuǎn)換

public class Person {public void run(){System.out.println("run");} } public class Student extends Person{public void go(){System.out.println("go");} } public class Teacher extends Person{ } public class Application {public static void main(String[] args) {// 類型之間的轉(zhuǎn)換 父 > 子// Person 高 Student 低Person obj = new Student(); // obj.go(); //報錯// student將這個對象轉(zhuǎn)換為Student類型，我們就可以使用Student類型的方法了 // Student student = (Student)obj; // student.go();// 簡寫((Student) obj).go();// 子類轉(zhuǎn)換為父類，可能丟失自己的本來的一些方法// 低轉(zhuǎn)高，直接轉(zhuǎn)換Student student1 = new Student();student1.go();Person person = student1;}} 多態(tài)1. 父類的引用指向子類的對象（子類的引用不能指向父類的對象）2. 把子類轉(zhuǎn)換為父類，向上轉(zhuǎn)型3. 把父類轉(zhuǎn)換為子類，向下轉(zhuǎn)換；強(qiáng)制轉(zhuǎn)換4. 方便方法的調(diào)用，減少重復(fù)的代碼，簡潔

https://www.bilibili.com/video/BV12J41137hu?p=72

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