java中instanceof與Class的等價性代碼示例

更新時間：2018年01月29日 10:11:05 作者：HeatDeath

這篇文章主要介紹了java中instanceof與Class的等價性代碼示例，小編覺得還是挺不錯的，具有一定借鑒價值，需要的朋友可以參考下

本文研究的主要是java中instanceof與Class的等價性的相關(guān)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(xiàn)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;

@Override
public void eat() {
 System.out.println("+++++++++");
}
}

主函數(shù)

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(jié)果：

true
false
true
true

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(nèi)容如下：

Testing x of type Base
-----------------------------------------
x instanceof Base true
x instanceof Derived false
-----------------------------------------
Base.isInstance(x) true
Derived.isInstance(x) false
-----------------------------------------
x.getClass() == Base.class true
x.getClass() == Derived.class false
x.getClass().equals(Base.class)) true
x.getClass().equals(Derived.class)) false
*****************************************
*****************************************
Testing x of type Derived
-----------------------------------------
x instanceof Base true
x instanceof Derived true
-----------------------------------------
Base.isInstance(x) true
Derived.isInstance(x) true
-----------------------------------------
x.getClass() == Base.class false
x.getClass() == Derived.class true
x.getClass().equals(Base.class)) false
x.getClass().equals(Derived.class)) true
*****************************************
*****************************************

Process finished with exit code 0

通過以上測試可以得出以下結(jié)論：