{"id":1187,"date":"2022-02-24T20:12:36","date_gmt":"2022-02-24T20:12:36","guid":{"rendered":"https:\/\/mdr.foobrdigital.com\/?p=1187"},"modified":"2022-02-24T20:12:36","modified_gmt":"2022-02-24T20:12:36","slug":"java-constructors","status":"publish","type":"post","link":"https:\/\/mudassirbackup.infinitycodestudio.com\/index.php\/2022\/02\/24\/java-constructors\/","title":{"rendered":"Java Constructors"},"content":{"rendered":"\n

In this tutorial, we will learn about Java constructors, their types, and how to use them with the help of examples.<\/p>\n\n\n\n

What is a Constructor?<\/h2>\n\n\n\n

A constructor in Java is similar to a method that is invoked when an object of the class is created.<\/p>\n\n\n\n

Unlike\u00a0Java methods, a constructor has the same name as that of the class and does not have any return type. For example,<\/p>\n\n\n\n

class Test {\n  Test() {\n    \/\/ constructor body\n  }\n}<\/code><\/pre>\n\n\n\n
Here, Test()<\/code> is a constructor. It has the same name as that of the class and doesn’t have a return type.<\/p>\n\n\n\n
<\/p>\n\n\n\n
\n\n\n\n
Example 1: Java Constructor<\/h2>\n\n\n\n
class Main {\n  private String name;\n\n  \/\/ constructor\n  Main() {\n    System.out.println(\"Constructor Called:\");\n    name = \"Programiz\";\n  }\n\n  public static void main(String[] args) {\n\n    \/\/ constructor is invoked while\n    \/\/ creating an object of the Main class\n    Main obj = new Main();\n    System.out.println(\"The name is \" + obj.name);\n  }\n}<\/code><\/pre>\n\n\n\n
Output<\/strong>:<\/p>\n\n\n\n
Constructor Called:\nThe name is Programiz<\/samp><\/code><\/pre>\n\n\n\n
In the above example, we have created a constructor named Main()<\/code>. Inside the constructor, we are initializing the value of the name<\/var> variable.<\/p>\n\n\n\n
Notice the statement of creating an object of the Main<\/var> class.<\/p>\n\n\n\n
Main obj = new Main();<\/code><\/pre>\n\n\n\n
Here, when the object is created, the Main()<\/code> constructor is called. And, the value of the name<\/var> variable is initialized.<\/p>\n\n\n\n
Hence, the program prints the value of the name<\/var> variables as Programiz<\/code>.<\/p>\n\n\n\n
\n\n\n\n
Types of Constructor<\/h3>\n\n\n\n
In Java, constructors can be divided into 3 types:<\/p>\n\n\n\n
  1. No-Arg Constructor<\/li>
  2. Parameterized Constructor<\/li>
  3. Default Constructor<\/li><\/ol>\n\n\n\n
    \n\n\n\n
    1. Java No-Arg Constructors<\/h2>\n\n\n\n
    Similar to methods, a Java constructor may or may not have any parameters (arguments).<\/p>\n\n\n\n
    If a constructor does not accept any parameters, it is known as a no-argument constructor. For example,<\/p>\n\n\n\n
    private Constructor() {\n   \/\/ body of the constructor\n}<\/code><\/pre>\n\n\n\n
    \n\n\n\n
    Example 2: Java private no-arg constructor<\/h3>\n\n\n\n
    class Main {\n\n  int i;\n\n  \/\/ constructor with no parameter\n  private Main() {\n    i = 5;\n    System.out.println(\"Constructor is called\");\n  }\n\n  public static void main(String[] args) {\n\n    \/\/ calling the constructor without any parameter\n    Main obj = new Main();\n    System.out.println(\"Value of i: \" + obj.i);\n  }\n}<\/code><\/pre>\n\n\n\n
    Output<\/strong>:<\/p>\n\n\n\n
    Constructor is called\nValue of i: 5<\/samp><\/code><\/pre>\n\n\n\n
    In the above example, we have created a constructor Main()<\/code>. Here, the constructor does not accept any parameters. Hence, it is known as a no-arg constructor.<\/p>\n\n\n\n
    Notice that we have declared the constructor as private.<\/strong><\/p>\n\n\n\n
    Once a constructor is declared private<\/code>, it cannot be accessed from outside the class. So, creating objects from outside the class is prohibited using the private constructor.<\/p>\n\n\n\n
    Here, we are creating the object inside the same class. Hence, the program is able to access the constructor. <\/p>\n\n\n\n
    However, if we want to create objects outside the class, then we need to declare the constructor as public<\/code>.<\/p>\n\n\n\n
    Example 3: Java public no-arg constructors<\/h3>\n\n\n\n
    class Company {\n  String name;\n\n  \/\/ public constructor\n  public Company() {\n    name = \"Programiz\";\n  }\n}\n\nclass Main {\n  public static void main(String[] args) {\n\n    \/\/ object is created in another class\n    Company obj = new Company();\n    System.out.println(\"Company name = \" + obj.name);\n  }\n}<\/code><\/pre>\n\n\n\n
    Output<\/strong>:<\/p>\n\n\n\n
    Company name = Programiz<\/samp><\/code><\/pre>\n\n\n\n
    Recommended Reading:<\/strong>\u00a0Java Access Modifier<\/p>\n\n\n\n
    \n\n\n\n
    2. Java Parameterized Constructor<\/h2>\n\n\n\n
    A Java constructor can also accept one or more parameters. Such constructors are known as parameterized constructors (constructor with parameters).<\/p>\n\n\n\n
    Example 4: Parameterized constructor<\/h3>\n\n\n\n
    class Main {\n\n  String languages;\n\n  \/\/ constructor accepting single value\n  Main(String lang) {\n    languages = lang;\n    System.out.println(languages + \" Programming Language\");\n  }\n\n  public static void main(String[] args) {\n\n    \/\/ call constructor by passing a single value\n    Main obj1 = new Main(\"Java\");\n    Main obj2 = new Main(\"Python\");\n    Main obj3 = new Main(\"C\");\n  }\n}<\/code><\/pre>\n\n\n\n
    Output<\/strong>:<\/p>\n\n\n\n
    Java Programming Language\nPython Programming Language\nC Programming Language<\/samp><\/code><\/pre>\n\n\n\n
    In the above example, we have created a constructor named Main()<\/code>. Here, the constructor takes a single parameter. Notice the expression,<\/p>\n\n\n\n
    Main obj1 = new Main(\"Java\");<\/code><\/pre>\n\n\n\n
    Here, we are passing the single value to the constructor. Based on the argument passed, the language variable is initialized inside the constructor.<\/p>\n\n\n\n
    \n\n\n\n
    3. Java Default Constructor<\/h2>\n\n\n\n
    If we do not create any constructor, the Java compiler automatically create a no-arg constructor during the execution of the program. This constructor is called default constructor.<\/p>\n\n\n\n
    Example 5: Default Constructor<\/h3>\n\n\n\n
    class Main {\n\n  int a;\n  boolean b;\n\n  public static void main(String[] args) {\n\n    \/\/ A default constructor is called\n    Main obj = new Main();\n\n    System.out.println(\"Default Value:\");\n    System.out.println(\"a = \" + obj.a);\n    System.out.println(\"b = \" + obj.b);\n  }\n}<\/code><\/pre>\n\n\n\n
    Output<\/strong>:<\/p>\n\n\n\n
    a = 0\nb = false<\/samp><\/code><\/pre>\n\n\n\n
    Here, we haven’t created any constructors. Hence, the Java compiler automatically creates the default constructor.<\/p>\n\n\n\n
    The default constructor initializes any uninitialized instance variables with default values.<\/p>\n\n\n\n
    Type<\/th>Default Value<\/th><\/tr>
    boolean<\/code><\/td>false<\/td><\/tr>
    byte<\/code><\/td>0<\/td><\/tr>
    short<\/code><\/td>0<\/td><\/tr>
    int<\/code><\/td>0<\/td><\/tr>
    long<\/code><\/td>0L<\/td><\/tr>
    char<\/code><\/td>\\u0000<\/td><\/tr>
    float<\/code><\/td>0.0f<\/td><\/tr>
    double<\/code><\/td>0.0d<\/td><\/tr>
    object<\/code><\/td>Reference null<\/td><\/tr><\/tbody><\/table><\/figure>\n\n\n\n
    In the above program, the variables a<\/var> and b<\/var> are initialized with default value 0<\/strong> and false<\/code> respectively.<\/p>\n\n\n\n
    The above program is equivalent to:<\/p>\n\n\n\n
    class Main {\n\n  int a;\n  boolean b;\n\n  \/\/ a private constructor\n  private Main() {\n    a = 0;\n    b = false;\n  }\n\n  public static void main(String[] args) {\n    \/\/ call the constructor\n    Main obj = new Main();\n\n    System.out.println(\"Default Value:\");\n    System.out.println(\"a = \" + obj.a);\n    System.out.println(\"b = \" + obj.b);\n  }\n}<\/code><\/pre>\n\n\n\n
    The output of the program is the same as Example 5.<\/strong><\/p>\n\n\n\n
    \n\n\n\n
    Important Notes on Java Constructors<\/h2>\n\n\n\n
    • Constructors are invoked implicitly when you instantiate objects.<\/li>
    • The two rules for creating a constructor are:
      The name of the constructor should be the same as the class.
      A Java constructor must not have a return type.<\/li>
    • If a class doesn’t have a constructor, the Java compiler automatically creates a default constructor<\/strong> during run-time. The default constructor initializes instance variables with default values. For example, the int<\/code> variable will be initialized to 0<\/code><\/li>
    • Constructor types:
      No-Arg Constructor<\/strong> – a constructor that does not accept any arguments
      Parameterized constructor<\/strong> – a constructor that accepts arguments
      Default Constructor<\/strong> – a constructor that is automatically created by the Java compiler if it is not explicitly defined.<\/li>
    • A constructor cannot be abstract<\/code> or static<\/code> or final<\/code>.<\/li>
    • A constructor can be overloaded but can not be overridden.<\/li><\/ul>\n\n\n\n
      \n\n\n\n
      Constructors Overloading in Java<\/h2>\n\n\n\n
      Similar to\u00a0Java method overloading, we can also create two or more constructors with different parameters. This is called constructors overloading.<\/p>\n\n\n\n
      Example 6: Java Constructor Overloading<\/h3>\n\n\n\n
      class Main {\n\n  String language;\n\n  \/\/ constructor with no parameter\n  Main() {\n    this.language = \"Java\";\n  }\n\n  \/\/ constructor with a single parameter\n  Main(String language) {\n    this.language = language;\n  }\n\n  public void getName() {\n    System.out.println(\"Programming Langauage: \" + this.language);\n  }\n\n  public static void main(String[] args) {\n\n    \/\/ call constructor with no parameter\n    Main obj1 = new Main();\n\n    \/\/ call constructor with a single parameter\n    Main obj2 = new Main(\"Python\");\n\n    obj1.getName();\n    obj2.getName();\n  }\n}<\/code><\/pre>\n\n\n\n
      Output<\/strong>:<\/p>\n\n\n\n
      Programming Language: Java\nProgramming Language: Python<\/samp><\/code><\/pre>\n\n\n\n
      In the above example, we have two constructors: Main()<\/code> and Main(String language)<\/code>. Here, both the constructor initialize the value of the variable language with different values.<\/p>\n\n\n\n
      Based on the parameter passed during object creation, different constructors are called and different values are assigned.<\/p>\n\n\n\n
      It is also possible to call one constructor from another constructor. <\/p>\n","protected":false},"excerpt":{"rendered":"
      In this tutorial, we will learn about Java constructors, their types, and how to use them with the help of examples. What is a Constructor? A constructor in Java is similar to a method that is invoked when an object of the class is created. Unlike\u00a0Java methods, a constructor has the same name as that […]<\/p>\n","protected":false},"author":1,"featured_media":0,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[484],"tags":[],"_links":{"self":[{"href":"https:\/\/mudassirbackup.infinitycodestudio.com\/index.php\/wp-json\/wp\/v2\/posts\/1187"}],"collection":[{"href":"https:\/\/mudassirbackup.infinitycodestudio.com\/index.php\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/mudassirbackup.infinitycodestudio.com\/index.php\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/mudassirbackup.infinitycodestudio.com\/index.php\/wp-json\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/mudassirbackup.infinitycodestudio.com\/index.php\/wp-json\/wp\/v2\/comments?post=1187"}],"version-history":[{"count":0,"href":"https:\/\/mudassirbackup.infinitycodestudio.com\/index.php\/wp-json\/wp\/v2\/posts\/1187\/revisions"}],"wp:attachment":[{"href":"https:\/\/mudassirbackup.infinitycodestudio.com\/index.php\/wp-json\/wp\/v2\/media?parent=1187"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/mudassirbackup.infinitycodestudio.com\/index.php\/wp-json\/wp\/v2\/categories?post=1187"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/mudassirbackup.infinitycodestudio.com\/index.php\/wp-json\/wp\/v2\/tags?post=1187"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}