Question

What is the purpose of keyword new? Explain what happens when this keyword is used in an application.

Short answer

The 'new' keyword creates an instance of a class, allocates memory, and initializes the object via its constructor.

Step-by-step solution

Introduce the 'new' Keyword

In programming languages like Java, C++, and C#, the 'new' keyword is used to create new instances (objects) of a class.

Memory Allocation

When the 'new' keyword is used, the program requests memory from the heap to store the newly created object. This memory allocation is essential for the object to store data.

Constructor Invocation

After memory allocation, the constructor of the class is called. This constructor initializes the newly created object, setting up its initial state.

Reference Assignment

The 'new' keyword returns a reference to the memory address where the object is stored. This reference is typically assigned to a variable so the object can be accessed through that variable.

Key concepts

Memory Allocation

In Java, memory allocation is a crucial step that occurs when you create a new object using the `new` keyword. Think of this step as reserving a space for the object in a large memory warehouse called the heap. The heap is a pool of free memory, separate from the stack, specifically available for objects.

Memory allocation ensures that the new object has its own space in this warehouse where it can store data, such as variables or fields. The size of the memory allocated depends on the class definition of the object. Java automates memory management by handling allocation and deallocation through its garbage collection mechanism. This automation helps avoid common problems like memory leaks, allowing you to focus more on writing your code efficiently.

• Memory is allocated on the heap, not the stack.
• The amount of memory allocated depends on the object's class definition.
• Java uses garbage collection to manage memory automatically.

Constructor Invocation

Once memory is allocated, the next step in object creation is invoking the constructor. The constructor is a special method of the class that sets up the initial state of the object. It initializes the attributes (variables) of the object, ensuring that it's ready to be used right after its creation.

A constructor in Java can be a default one, or you can define your own to set specific parameters. A constructor does not have a return type and has the same name as the class. Its job is to perform any setup required to get the object into a valid state. For instance, it might set starting values or allocate resources the object needs right off the bat.

• Constructors initialize newly created objects.
• A constructor shares the same name as the class and does not return a value.
• Different constructors can be defined to initialize objects in various ways.

Reference Assignment

After memory is allocated and the constructor is completed, Java provides you with a reference to the new object. This reference is a memory address, essentially a way to locate the object in the heap, and it's crucial because it allows your program to access and interact with the object.

In practice, you assign this reference to a variable, which acts as a label for the object. For example, if you create a new `Car` object, you might store the reference in a variable called `myCar`. This variable then points to the memory space where the `Car` object resides, enabling your program to use it whenever needed. Without this reference, the object would be like a book buried somewhere in a vast library without a catalog entry.

• References point to the memory location of the object.
• Variables hold these references, acting as pointers to access objects.
• Reference assignment allows you to interact with and manipulate the object.