This is the default constructor… It doesn\u2019t do much except assigning default values to class variables.
\nThe default values of int data type is 0
\nThe default values of the String data type is null<\/div>\n
Java Parameterised Constructor<\/h4>\n
The real power of constructors can be leveraged by using parameterised constructors.<\/p>\n
A parameterised constructor allows passing a list of parameters in the constructor definition. Therefore, it gives an advantage to set the starting values of the object. Just like a method can have parameters of different data types, in the same way, a constructor can also have a parameter list of multiple data types.<\/p>\n
You can explicitly set the values of the class variables while declaring objects with the help of parameterised constructors.<\/p>\n
package com.dataflair.constructorsinjava\r\npublic class ConstructorTypes\r\n{\r\n int defaultvalueint;\r\n String defaultString;\r\n ConstructorTypes(int val, String value)\r\n {\r\n System.out.println(\"This is the parameterized constructor\");\r\n defaultString=value;\r\n defaultvalueint=val;\r\n }\r\n public static void main(String[] args) {\r\n\r\n ConstructorTypes object = new ConstructorTypes(52,\"DataFlair\");\/\/We called the default constructor here\r\n System.out.println(\"The default values of int data type is \"+object.defaultvalueint);\r\n System.out.println(\"The default values of the String data type is \"+object.defaultString);\r\n\r\n\r\n }\r\n}\r\n<\/pre>\nOutput:<\/strong><\/p>\nThis is the parameterized constructor
\nThe default values of int data type is 52
\nThe default values of the String data type is DataFlair<\/div>\n
A point to note would be that constructors cannot return values. However, you can return the instance of the current class with the help of constructors.<\/p>\n
Constructor Chaining in Java<\/h3>\n
As the name suggests, the chaining of constructors is simply calling a different constructor each time when the control shifts inside a particular constructor.<\/p>\n
Simply, it is the linking of multiple constructors in a class.<\/p>\n
You can achieve constructor chaining with the help of \u201cthis\u201d keyword.<\/p>\n
But why is this concept in practice? I mean, wouldn\u2019t it be easy to declare the constructors and call them individually anyway?<\/p>\n
Well yes, but constructor chaining particularly proves to be helpful when you need to do multiple tasks in a single constructor.<\/p>\n
The consecutive calls to the constructors help in defining each and every value.<\/p>\n
One important point to note is that the this() call should be before any other statement in the constructor. If not then the compiler returns an error.<\/p>\n
It is time for another example again!<\/p>\n
Java program to illustrate Java constructor chaining:<\/strong><\/p>\npackage com.dataflair.constructorsinjava;\r\npublic class ConstructorChaining {\r\n\r\n ConstructorChaining()\r\n {\r\n this(100);\r\n \/\/call made to constructor with one parameter of type int\r\n System.out.println(\"This is the default constructor \");\r\n\r\n }\r\n ConstructorChaining(int x)\r\n {\r\n this(x,\"DataFlair\");\r\n \/\/constructor call made with two parameters. \r\n System.out.println(\"This is a parameterized constructor\");\r\n\r\n\r\n }\r\n ConstructorChaining(int x, String s)\r\n {\r\n System.out.println(s+\" \"+x);\r\n System.out.println(\"This is the final constructor call. \");\r\n }\r\n public static void main(String[] args) {\r\n\r\n ConstructorChaining object = new ConstructorChaining();\r\n \r\n \r\n }\r\n}\r\n<\/pre>\nOutput:<\/strong><\/p>\nDataFlair 100
\nThis is the final constructor call.
\nThis is a parameterized constructor
\nThis is the default constructor<\/div>\n
Super Method in Java<\/h3>\n
When the super method gets executed, the control shifts to the constructor of the parent class.<\/p>\n
During the initialisation of a child class object, the compiler implicitly calls the superclass constructor.<\/p>\n
Let us see with an example<\/p>\n
Java program to illustrate the use of the super() method:<\/strong><\/p>\npackage com.dataflair.constructorsinjava;\r\nclass A\r\n{\r\n A()\r\n {\r\n System.out.println(\"This is the constructor of class A\");\r\n }\r\n\r\n}\r\nclass B extends A\r\n{\r\n B()\r\n {\r\n super();\r\n System.out.println(\"This is the constructor of class B\");\r\n }\r\n}\r\npublic class SuperConstructor {\r\n public static void main(String[] args) {\r\n \r\n B ob = new B();\r\n\r\n }\r\n}\r\n<\/pre>\nOutput:<\/strong><\/p>\nThis is the constructor of class A
\nThis is the constructor of class B<\/div>\n
Java Constructor Overloading<\/h3>\n
Similar to function overloading, constructor overloading involves the process of using the same name(which is evident because constructors and the classes share the same name), having different parameters.<\/p>\n
The compiler chooses the constructor based on the data types and the number of parameters. This process is similar to function overloading.<\/p>\n
Java program to illustrate the use of Constructor Overloading:<\/strong><\/p>\npackage com.dataflair.constructorsinjava;\r\nclass A\r\n{\r\n A()\r\n {\r\n System.out.println(\"This is the default constructor\");\r\n\r\n }\r\n A(int a)\r\n {\r\n System.out.println(\"This constructor consists of a single parameter of value \"+a);\r\n }\r\n A(int a, String s)\r\n {\r\n System.out.println(\"This constructor consists of two parameters of values \"+a+\", \"+s);\r\n }\r\n}\r\n\r\npublic class ConstructorOverloading {\r\n public static void main(String[] args) {\r\n \r\n A obj=new A();\r\n A obj1=new A(5,\"DataFlair\"); \r\n }\r\n \r\n\r\n}\r\n<\/pre>\nOutput:<\/strong><\/p>\nThis is the default constructor
\nThis constructor consists of two parameters of values 5, DataFlair<\/div>\n
Copy Constructor in Java<\/h3>\n
Java Copy constructors are particularly useful for copying the values of an object into a different object.<\/p>\n
Many a time, some objects need to have the same instance values. This is where copy constructors come in.<\/p>\n
Java program to illustrate the use of Copy Constructors:<\/strong><\/p>\npackage com.dataflair.constructorsinjava;\r\npublic class CopyConstructor {\r\n String s;\r\n CopyConstructor(String string)\r\n { \r\n this.s=string;\r\n\r\n }\r\n CopyConstructor(CopyConstructor object)\r\n {\r\n this.s=object.s;\r\n }\r\n public void valuesdisplay()\r\n {\r\n System.out.println(\"The object has the values-> \"+s);\r\n }\r\n public static void main(String[] args) {\r\n\r\n CopyConstructor object=new CopyConstructor(\"DataFlair\");\r\n CopyConstructor copyobject=new CopyConstructor(object);\r\n object.valuesdisplay();\r\n copyobject.valuesdisplay();\r\n\r\n \r\n }\r\n \r\n}\r\n<\/pre>\nOutput:<\/strong><\/p>\nThe object has the values-> DataFlair
\nThe object has the values-> DataFlair<\/div>\n
As you can see, the \u201ccopy object\u201d has the same values of instance variables as the primary object. This is possible due to copy constructors.<\/p>\n
Difference Between Java Constructors and Java Methods<\/h3>\n
\n\n\n| Constructors in Java<\/b><\/td>\n | Methods in Java<\/b><\/td>\n<\/tr>\n\n| Constructors must always have the same name as that of the class.<\/span><\/td>\n | The methods can have any name the programmer wants. However, it should not be an identifier or a reserved word.\u00a0<\/span><\/td>\n<\/tr>\n\n| Constructors cannot return a value. It can only return references.\u00a0<\/span><\/td>\n | Methods can return values.\u00a0<\/span><\/td>\n<\/tr>\n\n| The JVM invokes constructors implicitly whenever you create a new object.\u00a0<\/span><\/td>\n | You can call methods explicitly.\u00a0<\/span><\/td>\n<\/tr>\n\n| If no constructor is present, the JVM implicitly creates a default constructor.\u00a0<\/span><\/td>\n | If a method is not present, the JVM does not create default methods implicitly.\u00a0<\/span><\/td>\n<\/tr>\n\n| Constructors are particularly useful for initialising an object.\u00a0<\/span><\/td>\n | Methods are useful when you need to add specific functionality to an object.\u00a0<\/span><\/td>\n<\/tr>\n\n| A single constructor is non-inheritable by child classes.\u00a0<\/span><\/td>\n | Methods are inheritable by child classes.\u00a0<\/span><\/td>\n<\/tr>\n\n| A single class can have more than one constructor. But no two constructors can have the same parameters.\u00a0<\/span><\/td>\n | A single class can have more than one method. But no two methods can have the same name and the same parameters.\u00a0<\/span><\/td>\n<\/tr>\n\n| A constructor cannot be final, static or synchronizable.\u00a0<\/span><\/td>\n | Methods can be static, final or synchronised.\u00a0<\/span><\/td>\n<\/tr>\n<\/tbody>\n<\/table>\nPoints to Remember for Constructors in Java<\/h3>\n1. Firstly, the constructors should have the same name as the class.<\/p>\n 2. Constructors cannot return anything except a reference to the object.<\/p>\n 3. You can declare a constructor as private, protected, default or public.<\/p>\n 4. If there is no explicit mention of a constructor inside a class, the compiler will add a default constructor implicitly.<\/p>\n 5. If you are using this() or super(), care should be taken that these statements should be the first lines of code in the constructor scope.<\/p>\n 6. You can overload a constructor but you cannot override it.<\/p>\n 7. You cannot explicitly inherit a constructor.<\/p>\n 8. One cannot instantiate abstract classes. But they do have constructors. These constructors will be invoked when the class which implements the abstract class gets instantiated.<\/p>\n 9. The compiler would not insert a default constructor in the child class if the superclass doesn\u2019t have a default constructor.
\nthis() allows you to chain constructors together.<\/p>\n 10. The main difference between methods and constructors is that methods can return values and have a different name. But constructors have the same name as the class itself and can only return references. They cannot return values.<\/p>\n 11. Lastly, there are no constructors in interfaces.<\/p>\n Best Practices for Using the Constructor in Java<\/h3>\nConstructors in Java offer a powerful mechanism for initialising objects and ensuring their state is consistent upon creation. Here are some recommended practices to keep in mind when working with constructors:<\/p>\n 1. Favour Parameterised Constructors:<\/strong> While Java provides a default constructor if none is explicitly defined, it’s generally recommended to create parameterised constructors. This allows you to explicitly set the initial values of object properties during object creation, promoting better code clarity and maintainability.<\/p>\n2. Consider Constructor Chaining:<\/strong> Constructor chaining enables you to call one constructor from another within the same class. This can help initialise objects in a specific order or reuse common initialisation logic across multiple constructors.<\/p>\n3. Adhere to Naming Conventions:<\/strong> Although constructors share the class name, it’s still a good idea to follow standard naming conventions for Java methods. This promotes code readability and consistency within your project.<\/p>\nSummary<\/h3>\nIn this article, we learned about the various aspects of constructors in Java, its types and how to use them to our advantage.<\/p>\n Constructors may seem like an easy topic but interviewers manage to ask very tricky questions based on it. So it is extremely important to have a concrete knowledge of constructors during interviews.<\/p>\n","protected":false},"excerpt":{"rendered":" Constructors\u2026 The name itself is so creative in nature, isn\u2019t it? Well, constructors are basically the mould for objects. It gives the object its shape and meaning. Example time! If you ever visit a...<\/p>\n","protected":false},"author":5,"featured_media":84875,"comment_status":"open","ping_status":"closed","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[32],"tags":[2932,20823,2937,3709,7443,7466,7634,9097,9404],"class_list":["post-12260","post","type-post","status-publish","format-standard","has-post-thumbnail","hentry","category-java","tag-constructor-overloading-in-java","tag-constructor-vs-methods","tag-constructors-in-java","tag-default-constructor-in-java","tag-java-constructor-example","tag-java-default-constructor","tag-java-parameterized-constructor","tag-no-argument-constructor-in-java","tag-parameterized-constructor-in-java"],"yoast_head":"\n Constructor in Java with Example - DataFlair<\/title>\n<meta name=\"description\" content=\"Constructor in java is a block of code which creates an object. 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![\"Constructors](\"https:\/\/data-flair.training\/blogs\/wp-content\/uploads\/sites\/2\/2018\/03\/Constructors-in-Java.jpg\")
<\/a><\/p>\n