What is automatically provided for a class Java?
Constructor in java is used to create the instance of the class. Constructors are almost similar to methods except for two things - its name is the same as the class name and it has no return type. Sometimes constructors are also referred to as special methods to initialize an object. Show
Constructor in JavaWhenever we use
Here the first one is a constructor, notice that there is no return type and no return statement. The second one is a normal method where we are again calling the first constructor to get Employee instance and return it. It’s recommended to not have method name same as the class name because it creates confusion. Types of Constructor in JavaThere are three types of constructor in java.
Let’s look into all these constructor types with example programs. Default Constructor in JavaIt’s not required to always provide a constructor implementation in the class code. If we don’t provide a constructor, then java provides default constructor implementation for us to use. Let’s look at a simple program where default constructor is being used since we will not explicitly define a constructor.
No-Args ConstructorConstructor without any argument is called a no-args constructor. It’s like overriding the default constructor and used to do some pre-initialization stuff such as checking resources, network connections, logging, etc. Let’s have a quick look at the no-args constructor in java.
Now when we will call Parameterized ConstructorConstructor with arguments is called parameterized constructor. Let’s look at the example of parameterized constructor in java.
Constructor Overloading in JavaWhen we have more than one constructors, then it’s constructor overloading in java. Let’s look at an example of constructor overloading in java program.
Private Constructor in JavaNote that we can’t use abstract, final, static and synchronized keywords with constructors. However we can use access modifiers to control the instantiation of class object. Using
Constructor Chaining in JavaWhen a constructor calls another constructor of the same class, it’s called constructor chaining. We have to use
I have overridden the toString() method to print some useful information about Employee object. Below is the output produced by above program.
Notice how one constructor is being called from another constructor, that’s called constructor chaining process. Java Super ConstructorSometimes a class is inherited from a superclass, in that case, if we have to call superclass constructor then we can do it using
Now if we create a Student object like below;
What will be the output produced? The output of the above code will be:
So the
call went to the no-args constructor of Student class since there was no super call in the first statement the no-args or default constructor of Person class is called. Hence the output. What if we are using parameterized constructor of Student class as
Here the output is clear because we are explicitly calling superclass constructor, so Java doesn’t need to do any extra work from their side. Java Copy ConstructorJava copy constructor takes the object of the same class as an argument and creates a copy of it. Sometimes we need a copy of another object to do some processing. We can do this by following ways:
Now let’s see how to write a copy constructor. Suppose we have a class
Notice that
The output of the above program is:
Notice that when copy constructor is used, both the original object and its copy are unrelated to each other and any modifications in one of them will not reflect into other. That’s all for the constructor in java. What is automatically provided for a class if you do not write one yourself?Under what circumstances does Java automatically provide a default constructor for a class? If you do not write a constructor in a class then Java automatically provides a constructor when the class is compiled.
Does every class in Java automatically have a default constructor?All classes have constructors by default: if you do not create a class constructor yourself, Java creates one for you. However, then you are not able to set initial values for object attributes.
Which is called automatically when the A class instantiated?parent class constructor is called automatically when child class is instantiated in java [duplicate]
Which method is automatically called when an object is created?Constructors. Constructors are class methods that are executed automatically when an object of a given type is created. Constructors usually initialize the data members of the new object. A constructor can run only once when a class is created.
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