Question

What's the purpose of keyword new? Explain what happens when you use it.

Short answer

The keyword 'new' is used to create a new instance of a class, which entails allocating memory for the object and initializing it via the constructor.

Step-by-step solution

Understand the Purpose of 'new'

The keyword 'new' in many programming languages is used to create an instance of a class, which is effectively an object. When 'new' is used, it allocates memory space for the new object and returns a reference to that memory.

Initialize Object's State

After memory allocation, 'new' initializes the object by invoking the constructor of the class. The constructor is a special method in a class that sets up the initial state of the object, often accepting parameters to customize the creation.

Accessing the Object

Once the object is created and initialized, the reference returned by 'new' can be stored in a variable. This reference is then used to access the object's fields and methods.

Key concepts

Understanding Object Instantiation in Java

In Java, object instantiation is the process of creating a new instance of a class. When you instantiate an object, you're bringing it to life in a way that you can interact with it within your code. Imagine a class as a blueprint. Just like a house blueprint, it contains the details about how something should be created but isn't the item itself. To transform this blueprint into a physical entity, you use the keyword 'new'.

Through object instantiation, you can create as many objects (or houses, following our analogy) as you desire based on that single blueprint. Each object will have its own identity and set of properties, even though they're based on the same class. A real-world analogy would be manufacturing cars from the same design. Each car is a separate entity, just like objects instantiated from the same class.

Memory Allocation in Java

The concept of memory allocation in Java is a critical one, as it pertains to how the Java Virtual Machine (JVM) manages memory for you. When using the 'new' keyword, Java does two things: it allocates memory for the new object and then constructs the object in that space. Java has a storage area known as the heap, which is where all class instances (objects) are stored.

During memory allocation, the JVM determines the amount of space needed based on the object's class definition and sets that space aside in the heap. This is important because without this dedicated space, the object can't exist in your application. Moreover, Java manages this memory through a process called garbage collection, which automatically reclaims memory when objects are no longer in use, preventing memory leaks and helping to maintain an efficient memory management system.

Java Constructors

Now, let's focus on Java constructors. Java constructors are akin to a special type of method that Java calls when you create a new instance of a class. They have the same name as their class and no return type, not even void. Constructors can be overloaded, which means you can have more than one constructor in a class, each with different parameters to allow different ways of initializing an object.

When you use the 'new' keyword followed by the class name and parentheses, Java invokes the corresponding constructor. If you don't define a constructor, Java provides a default constructor that takes no arguments and doesn't do anything special. However, constructors can be designed to accept parameters so that you can set initial values for an object's fields when creating it. This process makes objects flexible and customizable right from the moment of their creation.