Parameterized Constructor in Java: A Beginner’s Guide with Code Examples

In Java, a constructor is a special method used to initialize objects. It is called when an instance of a class is created. Constructors have the same name as the class and do not have a return type, not even void. There are two types of constructors in the Java language. Default constructors and parameterized constructors. This article explains parameterized constructors.

What is Parameterized Constructor in Java?

A parameterized constructor is a constructor that takes one or more parameters to initialize an object with specific values when it is created. Using parameters, the developer can pass initial values to an object when it is instantiated. The parameterized constructors differ in terms of the parameters they hold. The compiler will not create a default constructor if the programmer creates their constructor.

Syntax of Parameterized Constructor

The Java class creates a default constructor if the programmer hasn’t defined any type of constructor in the class. The parameterized constructor has to be defined explicitly by the programmer. The main aim of creating a parameterized constructor is to initialize the objects with programmer-defined states or values. Members can be assigned during the initialization process with the help of parameterized constructors.

Examples

One can have any number of parameterized constructors in a class.

Example of Parameterized Constructor

The following program demonstrates the parameterized constructor in Java. Three constructors are implemented: one is a default constructor, and the other two are parameterized constructors.

During an object’s initialization, which constructor should be invoked depends upon the parameters passed. For example, when we create an object like nameClass ob  = new nameClass(“Harry”), the new keyword invokes parameterized constructors with a string parameter (nameClass(String)) after object initialization.

Program

Output

Example

Let’s look at some examples of parameterized constructors in Java.

Program

Output

Error Thrown by Default Constructor

If the programmer forgets to write a default constructor in the class, the compiler inserts the default constructor on its own. But if the programmer has written a constructor in the class, the compiler will not insert the default constructor in that class.

The following codes demonstrate the default constructor.

Program

Output

Program 2

Output

Also Read: Copy Constructor in Java

Difference Between Default Constructor and Parameterized Constructor in Java

Conclusion

Parameterized constructors are very useful tools in Java for the creation of objects with definite information at the stage of their creation. It helps developers to influence the state of an object by setting a value for the field and making the source code more understandable and orderly. Constructor overload allows the development of more than one constructor because each one is characteristic of a particular occasion of initialisation. Its use makes the design of your classes more flexible, efficient and easier to work with, particularly where complex applications are inherent.