The new keyword is used to create an object of a class.
- It allocates a memory to the object during runtime.
- It invokes the specified constructor of the class to create the object.
- It returns a reference to the allocated memory.
How to use the new keyword?
The following syntax is used to create an instance (object) of the class.
ClassName objectName = new ClassName();
For example:
// This statement will create the object of the // String class and the returned reference is // assigned to the object str. String str = new String();
Java new Keyword Example
Here, we have a class JavaExample, which contains a variable and a method. In order to access the variable and method, we need to create an object of this class. In this example, we have created an object obj of this class using new keyword.
public class JavaExample {
int num = 100; //variable
public void demo(){
System.out.println("hello");
}
public static void main(String[] args) {
JavaExample obj = new JavaExample();
System.out.println(obj.num);
obj.demo();
}
}
Output:
100 hello
In the above example, we have used the following statement to create the object.
JavaExample obj = new JavaExample();
This object creation can be divided into three parts:
Declaration: Class name followed by object name. This creates a reference of the class.
JavaExample obj
Instantiation: new keyword followed by the constructor of the class. This creates an object of the class, whose constructor is being called.
new JavaExample();
Initialization: Initializing the reference of class with the created object.
JavaExample obj = new JavaExample();
Example 2: Calling parameterized constructor to create object
In the above example, the new keyword calls the default constructor of the class, which is by default created for the each class. However if a class has a constructor that accepts arguments then we can pass the arguments while creating an instance of the class using new keyword.
public class JavaExample {
String myName;
int myAge;
JavaExample(String name, int age){
myName = name;
myAge = age;
}
public static void main(String[] args) {
JavaExample person = new JavaExample("Chaitanya", 35);
//Accessing the parameters of the created instance
System.out.println(person.myName);
System.out.println(person.myAge);
}
}
Output:
Chaitanya 35
Example 3: new keyword with array
Here, we are using the new keyword to create an array object.
public class JavaExample {
public static void main(String[] args) {
//int array arr of size 3
int arr[] = new int[3];
arr[0] = 101;
arr[1] = 102;
arr[2] = 103;
for(int i: arr){
System.out.println(i);
}
}
}
Output:
101 102 103
Example 4: new keyword with strings
We can also create an object of String class using new keyword. There is a difference between simple assignment and assignment using new, the difference is covered in Java String Tutorial.
public class JavaExample {
public static void main(String[] args) {
String s1 = new String("Hello");
String s2 = new String("World!");
System.out.println(s1+" "+s2);
}
}
Output:
Hello World!
Example 5: Creating an object of a collection class
We can also use new keyword to create object of various collection classes. In the following example, we are creating an object of ArrayList class.
import java.util.ArrayList;
public class JavaExample {
public static void main(String[] args) {
ArrayList<Integer> arrList = new ArrayList<>();
arrList.add(101);
arrList.add(201);
arrList.add(301);
arrList.add(401);
for(int i: arrList){
System.out.println(i);
}
}
}
Output:
