What is the difference between the instanceof keyword and the isInstance() method in Java?

The instanceof keyword and the isInstance() method are both used to check the class of an object, so what is the difference between them? The following article will help you understand the difference between the instanceof keyword and the isInstance() method. I hope it will be helpful to you.

The instanceof keyword and the isInstance() method are both used to check the object's class, and both return a Boolean value. But the main difference comes when we want to dynamically check the class of an object. In this case isInstance() method will work and this cannot be achieved through instanceof operator.

Let’s take a look at the difference between the instanceof keyword and the isInstance() method through examples.

Use instanceof keyword to check the class of the object

public class Test 
{ 
    public static void main(String[] args) 
    { 
        Integer i = new Integer(5); 
  
        // 当i是Integer类的实例时，输出true
        System.out.println(i instanceof Integer); 
    } 
}

Output:

true

Now, if we want to check the class of the object at runtime, then we have to use isInstance( )method.

public class Test 
{ 
    // 此方法告诉我们对象是否是以字符串“c”形式传递名称的类实例。
    public static boolean fun(Object obj, String c) 
                      throws ClassNotFoundException 
    { 
        return Class.forName(c).isInstance(obj); 
    } 
    public static void main(String[] args) 
                      throws ClassNotFoundException 
    { 
        Integer i = new Integer(5); 
  
        // 当i是Integer类的实例时，输出true
        boolean b = fun(i, "java.lang.Integer"); 
  
        // 因为i不是String类的实例，所以输出false
        boolean b1 = fun(i, "java.lang.String"); 
  
        //当integer类扩展number类时，如果我也是number类的实例，则输出true。
        boolean b2 = fun(i, "java.lang.Number"); 
  
        System.out.println(b); 
        System.out.println(b1); 
        System.out.println(b2); 
    } 
}

Output:

true
false
true

Note: If we check the object using other classes that are not instantiated, the instanceof keyword will throw a compile-time error (incompatible condition operand type).

public class Test 
{ 
    public static void main(String[] args) 
    { 
        Integer i = new Integer(5); 
  
        //报错，因为类型不兼容：Integer不能转换为String
        System.out.println(i instanceof String); 
    } 
}

Output:

demo.java:10: error: incompatible types: Integer cannot be converted to String
System.out.println(i instanceof String); 
                   ^
1 error

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