The meaning and usage of instanceof

first, let's explain what instanceof is, Instanceof is a two-dollar operator (operator) of Java and PHP, and ==,>,< is the same kind of thing. Because it is made up of letters, it is also a reserved keyword for Java . Its function is to determine whether its left object is an instance of its right class and returns a Boolean type of data. Can be used to determine whether an instance of a subclass in an inheritance is an implementation of a parent class. Equivalent to the IS operator in C #. The instanceof operator in Java is used to indicate at run time whether an object is an instance of a particular class. Instanceof Indicates whether this object is an instance of this particular class or its subclasses by returning a Boolean value.

Next I will explain the meaning and usage of instanceof from four aspects:

First, usage

Boolean result = Object instanceof class

Second, the parameters

Result: Boolean type.

Object: Required option. An arbitrary object expression.

Class: Required option. Any of the defined object classes.

Third, the description

If object is an instance of class, the instanceof operator returns TRUE. Returns False if object is not an instance of the specified class, or if object is null.

Iv..

Package com.instanceoftest;

Interface a{}

Class B implements a{}

Class C extends B {}

Class Instanceoftest {

public static void Main (string[] args) {

A A=null;

B B=null;

Boolean res;

System.out.println ("Instanceoftest test Case 1:------------------");

res = a instanceof A;

System.out.println ("A instanceof A:" + res);
　　
res = b instanceof B;
System.out.println ("b instanceof B:" + res);

System.out.println ("\ninstanceoftest test Case 2:------------------");

A=new B ();

B=new B ();

res = a instanceof A;

System.out.println ("A instanceof A:" + res);

res = a instanceof B;

System.out.println ("A instanceof B:" + res);

res = b instanceof A;

System.out.println ("b instanceof A:" + res);

res = b instanceof B;

System.out.println ("b instanceof B:" + res);

System.out.println ("\ninstanceoftest test Case 3:------------------");

b b2= (b) New C ();

res = B2 instanceof A;

System.out.println ("B2 instanceof A:" + res);

res = B2 instanceof B;

System.out.println ("B2 instanceof B:" + res);

res = B2 instanceof C;

System.out.println ("B2 instanceof C:" + res);

}
}

/*result:

Instanceoftest test Case 1:------------------

A instanceof A:false

b instanceof B:false

Instanceoftest test Case 2:------------------

A instanceof A:true

A instanceof B:true

b instanceof A:true

b instanceof B:true

Instanceoftest test Case 3:------------------

B2 instanceof A:true

B2 instanceof B:true

B2 instanceof C:true

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The meaning and usage of instanceof