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2010-06-01T04:57:57Z

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в 17:44, 31 мая 2010

2010-05-31T17:44:27Z

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== Finding Out of what Class an Object is Instantiated ==



<source lang="java">
import java.util.ArrayList;
import java.util.Vector;
public class Main {
public static void main(String[] args) {
Object testObject = new Vector();
if (testObject instanceof Vector)
System.out.println("Object was an instance of the class java.util.Vector");
else if (testObject instanceof ArrayList)
System.out.println("Object was an instance of the class java.util.ArrayList");
else
System.out.println("Object was an instance of the " + testObject.getClass());
}
}
//Object was an instance of the class java.util.Vector</source>



== Identifying Objects ==



<source lang="java">
class Animal {
public String toString() {
return "This is an animal ";
}
}
class Dog extends Animal {
public void sound() {
System.out.println("Woof Woof");
}
}
public class MainClass {
public static void main(String[] a) {
Dog aDog = new Dog();
if (aDog instanceof Animal) {
Animal ani = (Animal) aDog;
System.out.println(ani);
}
}
}</source>



<pre class=codeResult>This is an animal</pre>

== instanceof operator and class hierarchy ==



<source lang="java">
class A {
int i, j;
}
class B {
int i, j;
}
class C extends A {
int k;
}
class D extends A {
int k;
}
class InstanceOf {
public static void main(String args[]) {
A a = new A();
B b = new B();
C c = new C();
D d = new D();
if (a instanceof A)
System.out.println("a is instance of A");
if (b instanceof B)
System.out.println("b is instance of B");
if (c instanceof C)
System.out.println("c is instance of C");
if (c instanceof A)
System.out.println("c can be cast to A");
if (a instanceof C)
System.out.println("a can be cast to C");
System.out.println();
A ob;
ob = d; // A reference to d
System.out.println("ob now refers to d");
if (ob instanceof D)
System.out.println("ob is instance of D");
System.out.println();
ob = c; // A reference to c
System.out.println("ob now refers to c");
if (ob instanceof D)
System.out.println("ob can be cast to D");
else
System.out.println("ob cannot be cast to D");
if (ob instanceof A)
System.out.println("ob can be cast to A");
System.out.println();
// all objects can be cast to Object
if (a instanceof Object)
System.out.println("a may be cast to Object");
if (b instanceof Object)
System.out.println("b may be cast to Object");
if (c instanceof Object)
System.out.println("c may be cast to Object");
if (d instanceof Object)
System.out.println("d may be cast to Object");
}
}</source>



== The instanceof Keyword ==

<p>The instanceof keyword can be used to test if an object is of a specified type.</p>



<source lang="java">
if (objectReference instanceof type)</source>



<pre class=codeResult>true</pre>

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Java Tutorial/Operators/instanceof - История изменений

Admin: 1 версия

в 17:44, 31 мая 2010