new Keyword in Java (Usage and Examples)

The Java `new` keyword creates a class instance by allocating dynamic memory for a new object and returns a reference to that memory. It can also be used to create an array object. When the `new` keyword is employed, it executes the class constructor to initialize the object. So, the new keyword is important in Java, as it creates an instance of the class.

Syntax:

Usage of new Keyword

• It instantiates a class and calls its constructor.
• It initialises an array and allocates memory for it.
• It is also useful for creating anonymous objects.
• It can create instances of inner classes.
• When no parameters are passed, it uses the default constructor.

Java new Keyword Examples

Creating an Object

Output:

Invoking Method

Explanation

In the above program, we defined a class named Main. Inside the Main class, we declared and defined a method named display(). To invoke the display() method, we first created an object of the Main class in the main() method using the new keyword. We invoked the display() method with that object, which prints 'Invoking Method' on the console.

Creating an Object with a Default Constructor

Output:

Invoking Constructor

Explanation

In the above program, we defined a class named Main. Inside the Main class, there is a default constructor. Within the constructor, there is only a print statement. In the main() method, we have created an object of the Main class that automatically calls the default constructor, which prints 'Invoking Constructor' on the console.

Creating an Object with a Parameterized Constructor

Output:

30

Explanation

In the above program, we defined a class named Main. Inside the Main class, there is a parameterized constructor that has two parameters, a and b of type integer, and a method named display(). Inside the main() method, we have created an object of the Main class by using the new keyword and passed the parameters in the constructor. When we invoke the display() method, it prints 30 on the console.

Creating an Array

Output:

Array length: 3

Explanation

In the above program, we defined a class named Main in which an instance of an array (of size 3) is created by using the new keyword. The print statement accesses the length property of the arr[] array that returns the size of the array (in this case, 3), and prints it Array length: 3 on the console.

Creating Collection

Output:

[Java, C++, Python]

Explanation

In the above program, we created an object of the ArrayList class using the new keyword and added elements to it. The print statement outputs the elements to the console.

Important Points to Remember

1. The new keyword is used to create an instance of a class (an object). Without it, objects cannot be instantiated.
2. It allocates memory for the object on the heap, ensuring there is space to store its fields and methods.
3. When we use the new keyword, it automatically calls the constructor (default) of the class to initialize the object.
4. The new keyword returns a reference to the newly created object, which can be stored in a variable.
5. It is also utilized to allocate memory for arrays, including both primitive and object types.
6. We can use new to create instances of inner classes, which require an instance of the outer class.
7. It allows for the creation of anonymous objects.
8. The new keyword can be employed with polymorphic references, where the reference type is a parent class or interface.

Java new Keyword MCQ

1. What does the new keyword in Java?

1. Modifies an Object
2. Delete an Object
3. Creates an Object
4. Makes Object Mutable

2. Which of the following is true about the new Keyword?

1. It allocates memory for an object
2. It initializes an object
3. Both 1 and 2
4. Both 2 and 3

3. What happens if we use the new keyword without assigning it to a reference variable?

1. An object is created, but becomes unreachable
2. An object is not created
3. The program throws an error
4. None of the above

4. How many objects will be created in the following?

1. 4
2. 3
3. 2
4. 1

5. Select a valid statement for the creation of an integer array.

1. int arr[] = new int();
2. int arr[] = new int[3];
3. int arr[] = new int[];
4. int arr[] = new int(3);