java中instanceof與Class的等價性代碼示例

2024-07-13 10:17:28

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本文研究的主要是java中instanceof與Class的等價性的相關問題，具體如下。

java 中的instanceof 運算符是用來在運行時指出對象是否是特定類的一個實例。instanceof通過返回一個布爾值來指出，這個對象是否是這個特定類或者是它的子類的一個實例。

實例1（instanceof）

接口Person

public interface Person {public void eat();}

實現類People

public class People implements Person {private int a=0; @Override public void eat() { System.out.println("======"+a);  }}

子類xiaoming：

public class xiaoming extends People {private String name;@Overridepublic void eat() { System.out.println("+++++++++");}}

主函數

public static void main(String[] args) { People p=new People(); xiaoming x=new xiaoming(); System.out.println(p instanceof Person); System.out.println(p instanceof xiaoming); -----2 System.out.println(x instanceof Person); System.out.println(x instanceof People); }

注意：上面2處的代碼在編譯時不會報錯。

運行結果：

truefalsetruetrue

實例2

package com.test.class_obj;class Base {}class Derived extends Base {}public class FamilyVsExactType {	static void test(Object x) {		System.out.println("Testing x of type " + x.getClass().getSimpleName());		System.out.println("-----------------------------------------");		System.out.println("x instanceof Base " + (x instanceof Base));		System.out.println("x instanceof Derived " + (x instanceof Derived));		System.out.println("-----------------------------------------");		System.out.println("Base.isInstance(x) " + Base.class.isInstance(x));		System.out.println("Derived.isInstance(x) " +		        Derived.class.isInstance(x));		System.out.println("-----------------------------------------");		System.out.println("x.getClass() == Base.class " +		        (x.getClass() == Base.class));		System.out.println("x.getClass() == Derived.class " +		        (x.getClass() == Derived.class));		System.out.println("x.getClass().equals(Base.class)) " +		        (x.getClass().equals(Base.class)));		System.out.println("x.getClass().equals(Derived.class)) " +		        (x.getClass().equals(Derived.class)));		System.out.println("*****************************************");		System.out.println("*****************************************");	}	public static void main(String[] args) {		test(new Base());		test(new Derived());	}}

輸出內容如下：

Testing x of type Base-----------------------------------------x instanceof Base truex instanceof Derived false-----------------------------------------Base.isInstance(x) trueDerived.isInstance(x) false-----------------------------------------x.getClass() == Base.class truex.getClass() == Derived.class falsex.getClass().equals(Base.class)) truex.getClass().equals(Derived.class)) false**********************************************************************************Testing x of type Derived-----------------------------------------x instanceof Base truex instanceof Derived true-----------------------------------------Base.isInstance(x) trueDerived.isInstance(x) true-----------------------------------------x.getClass() == Base.class falsex.getClass() == Derived.class truex.getClass().equals(Base.class)) falsex.getClass().equals(Derived.class)) true**********************************************************************************Process finished with exit code 0

通過以上測試可以得出以下結論：