You must be aware of creating an object of a class by using the new keyword, but that is not the only way to create an Object.
There are several other ways to create an object of a class :
- Using new keyword
- Using new Instance (Reflection)
- Using Clone
- Using Deserialization
- Using ClassLoader
- … don’t know 🙂
Using new Keyword
Using a new keyword is the most basic way to create an object. new keyword can be used to create an object of a class.
public class ObjectCreationExample {
public static void main(String[] args) {
// Here we are creating Object of JBT using new keyword
JBT obj = new JBT();
}
}
class JBT{
String Owner;
}
Using New Instance (Reflection)
Have you ever tried to connect to a DB using the JDBC driver in Java? If your answer is yes, then you must have seen “Class.forName“. We can also use it to create the object of a class. Class.forName actually loads the class in java but doesn’t create any object. To create an object, you have to use the newInstance method of the Class class.
/*
* Here we will learn to create Object of a class without using new Operator.
* But newInstance method of Class class.
*/
class CreateObject {
public static void main(String[] args) {
try {
Class cls = Class.forName("JBTClass");
JBTClass obj = (JBTClass) cls.newInstance();
JBTClass obj1 = (JBTClass) cls.newInstance();
System.out.println(obj);
System.out.println(obj1);
} catch (ClassNotFoundException e) {
e.printStackTrace();
} catch (InstantiationException e) {
e.printStackTrace();
} catch (IllegalAccessException e) {
e.printStackTrace();
}
}
}
class JBTClass {
static int j = 10;
JBTClass() {
i = j++;
}
int i;
@Override
public String toString() {
return "Value of i :" + i;
}
}
If you want to create the object in this way class needs to have a public default constructor.
Using Clone
We can also use Clone() method to create a copy of an existing object.
/*
* Here we will learn to create an Object of a class without using new Operator.
* For this purpose we will use Clone Interface
*/
class CreateObjectWithClone {
public static void main(String[] args) {
JBTClassClone obj1 = new JBTClassClone();
System.out.println(obj1);
try {
JBTClassClone obj2 = (JBTClassClone) obj1.clone();
System.out.println(obj2);
} catch (CloneNotSupportedException e) {
e.printStackTrace();
}
}
}
class JBTClassClone implements Cloneable {
@Override
protected Object clone() throws CloneNotSupportedException {
return super.clone();
}
int i;
static int j = 10;
JBTClassClone() {
i = j++;
}
@Override
public String toString() {
return "Value of i :" + i;
}
} Additional notes on Clone
- Here we are creating the clone of an existing Object and not any new Object.
- The clone method is declared protected in Object class. So it can be accessed only in a subclass or in the same package. That is the reason why it has been overridden here in class.
- A class needs to implement the Cloneable interface otherwise it will throw CloneNotSupportedException.
Using Object Deserialization
Object deserialization can also be used to create an Object. It produces the opposite of serializing an Object.
Using ClassLoader
We can also use ClassLoader to create the object of a class. This way is much the same as Class.forName option.
/*
* Here we will learn to Create an Object using Class Loader
*/
public class CreateObjectWithClassLoader {
public static void main(String[] args) {
JBTClassLoader obj = null;
try {
obj = (JBTClassLoader) new CreateObjectWithClassLoader().getClass()
.getClassLoader().loadClass("JBTClassLoader").newInstance();
// Fully qualified classname should be used.
} catch (InstantiationException e) {
e.printStackTrace();
} catch (IllegalAccessException e) {
e.printStackTrace();
} catch (ClassNotFoundException e) {
e.printStackTrace();
}
System.out.println(obj);
}
}
class JBTClassLoader {
static int j = 10;
JBTClassLoader() {
i = j++;
}
int i;
@Override
public String toString() {
return "Value of i :" + i;
}
}
Java is quite a nice language. It’s annoying that it’s useless to have a language without pointers. Good guide, but throw Java in the trash. A pebble is more useful than Java 🙁
Disagree
thanks for u r explanation.its very useful
very useful.Thanks
You need to mention your class file package thats why you are getting not found excepction
Is there any difference between :
Clone :-
JBTClassClone obj1 = new JBTClassClone();
JBTClassClone obj2 = (JBTClassClone) obj1.clone();
And just copying object :-
JBTClassClone obj = new JBTClassClone();
JBTClassClone obj1 = obj;
There is difference. In first case you are creating clone of object and then assigning while in second you are not creating any clone and assigning the same object to new reference.
I have code as bellow:
package com.ex.helloworld;
public class HelloWorld {
public static void main(String []args){
TestLoader obj = null;
try {
obj = (TestLoader) new HelloWorld().getClass().getClassLoader().loadClass(“TestLoader”).newInstance();
} catch (InstantiationException | IllegalAccessException | ClassNotFoundException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
System.out.println(“TestLoader: “+ obj.toString());
}
}
class TestLoader{
static int j = 10;
int i;
public TestLoader() {
i = ++j;
}
@Override
public String toString(){
return “Value Of i: “+ i;
}
}
But when I run , I have a error:
java.lang.ClassNotFoundException: TestLoader
at java.net.URLClassLoader$1.run(Unknown Source)
at java.net.URLClassLoader$1.run(Unknown Source)
at java.security.AccessController.doPrivileged(Native Method)
at java.net.URLClassLoader.findClass(Unknown Source)
at java.lang.ClassLoader.loadClass(Unknown Source)
at sun.misc.Launcher$AppClassLoader.loadClass(Unknown Source)
at java.lang.ClassLoader.loadClass(Unknown Source)
at com.ex.helloworld.HelloWorld.main(HelloWorld.java:9)
Exception in thread “main” java.lang.NullPointerException
at com.ex.helloworld.HelloWorld.main(HelloWorld.java:16)
What problem with my code ?
your program answer 11. your program is correct please check once at “TestLoader” and return “value of i:”+i;( its double quotation )
Class.forName() is throwing exception. Its not working
java.lang.ClassNotFoundException:
Class.forName() in my code also throws java.lang.ClassNotFoundException, I don’t know why
You need to provide the package name also make your class public.
@Dev: you need to mention the fully qualified class name like this:
Class cls = Class.forName(“com.test.JBTClass”);
Give the full qualified name of the class
The fully qualified name of the class is
Predefined classes are organize in package
So, before using the class in your program you must give fully qualified name to that class
Egl
int double y=Java.util.math.squar(y);
Here
Square is method name of class math
Math is class in until package
Java is language name or system
hi,
i have an doubt what is the difference creating the object using class loader and using new instance both same know.please give me some more detailed explanation regarding that.
thanks in advance..
through class loader it is not working.i mean showing exception with null value.
public class Testing {
public static void main(String[] args) {
Testing obj = null;
{
try {
obj = (Testing) new Testing().getClass()
.getClassLoader().loadClass(“Testing”).newInstance();
// Fully qualified classname should be used.
} catch (ClassNotFoundException | InstantiationException | IllegalAccessException ex) {
Logger.getLogger(Testing.class.getName()).log(Level.SEVERE, null, ex);
}
System.out.println(obj);
}
}
}
lol