java 判斷類和實例的關系(instanceof,isInstance,isAssignableFrom)

判斷類與實例的關系有以下三種方式 

1、instanceOf關鍵字，用來判斷對象是否是類的實例 
2、isAssignableFrom，用來判斷類型間是否存在派生關系 
3、isInstance方法，用來判斷對象是否屬於某個類型的實例 

 

        //use instanceOf，用來判斷對象是否是類的實例
        System.out.println(new A() instanceof B);//類型比較

        //use isAssignableFrom()，用來判斷類型間是否有繼承關系

        System.out.println(B.class.isAssignableFrom(A.class));
 
        //use isInstance()，用來判斷對象是否是類的實例

        System.out.println(A.class.isInstance(new A（）));//class比較

 

import java.util.Date;

public class Program
{
    public static void main(String[] args)
    {
        // Get the Class object associated with Integer.
        Class intClass = Integer.class;

        // Create various objects.
        String str = "Hello";
        Date date = new Date();
        Integer i = new Integer(10);

        // Is str an instance of class Integer?
        boolean check1 = intClass.isInstance(str);
        System.out.println("str is an Integer? " + check1);

        // Is date an instance of class Integer?
        boolean check2 = intClass.isInstance(date);
        System.out.println("date is an Integer? " + check2);

        // Is i an instance of class Integer?
        boolean check3 = intClass.isInstance(i);
        System.out.println("i is an Integer? " + check3);
    }
}

/*
Output:
str is an Integer? false
date is an Integer? false
i is an Integer? true
*/