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Answered 2009-07-19 04:41:58

No. If you do not write a constructor for you classes, the default Object constructor can still be used.

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The default constructor is an empty (only call the super constructor) with no parameters constructor inserted by the java compiler when you don't define a constructor in your class. If you write something like this: public class NoConstructorClass{ //no constructor goes here } Then you get something like this: public class NoConstructorClass{ public NoConstructorClass(){ // Default constructor that you didn't write super(); } }


When we want to create an Object for a class at that time we will write constructor.


A constructor of a class in invoked when a object of that class is created. As an abstract class can't have an object, so we can't create a constructor of the abstract class. But we can create a constructor of a concrete subclass of that abstract class and we have to pass the object of that concrete subclass to the abstract class.


Any time you don't write any constructor for your class, the compiler supplies the default constructor. In other words, if you wrote a constructor the compiler won't.


Both are functions, i.e., places where you can write code. A constructor is simply a special method that is invoked automatically when an object is created.


The first thing to note about constructor overloading is that Java creates a no argument constructor for you if and only if you have not typed a constructor yourself. Every class has a constructor even abstract ones (default no argument constructor). Abstract constructors are always executed. To overload a constructor you can do the following: class Test { String name; Test(String n) { name = n; System.out.println("Constructing Test Object named: " + name); } } In the case above we are overloading the default no argument constructor with a constructor that takes a String parameter. You can write you own no argument constructor as follows: class Test { Test() { System.out.println("Constructing Test Object"); } } To override our own no argument constructor we do this: class Test { Test() { // our no argument constructor System.out.println("Constructing Test Object"); } String name; Test(String n) { // overloading our no argument constructor with this // constructor that take a String parameter name = n; System.out.println("Constructing Test Object named: " + name); } }


Nothing Happens. Actually such a constructor is called a Default Constructor. Even if we do not write a constructor for a class, Java would automatically place a default constructor inside the class. Ex: Public class Test { public String getName(){ return "Hi"; } } Public class TestEx { public static void main(String[] args){ Test obj = new Test(); System.out.println(obj.getName()); } } Here we were able to instantiate an object of class Test even though we did not define a constructor for that class. This is because Java automatically places a default constructor for the class.


when we write a new keyword with any class, then it calls the immediate super class constructor and then it object is created.


if we write a code in java then we don't mansion a default constructor in it then compiler by default provide a default constructor and the main impotent role of default constructor in our program is that it initialize the member of the class then it is reason compiler provide a default constructor in our java program code .


A constructor lets you write code that will be executed when the class is instantiated with the "new" keyword.


Assuming class A has a method named getXXX() and class B is a sub class of class A. Now, if we write a method with the same name getXXX() in class B, with exactly the same signature as class A, it is called overriding a method. The method getXXX() in class A becomes the overridden method.


These are two different things. "Super" is used in inheritance - if class B inherits from class A, and we want the constructor of B to do the same things the constructor of A does (and maybe more things), we can call A's constructor in B's constructor: public B() { super(); ...... } Notice that it must be the first line in B's constructor. "This" is used in case of overloading, to call a function aith the same name. For example, if we have a constructor that receives one argument, and we it want to have a default value of 0, we can write: public C() { this(0); }


Constructors in java cannot be invoked explicitly. They are invoked automatically when an object is created. In java if u dont write any code for constructor, by default compiler inserts a zero argument constructor. If required, it can be overrided.


Yes you can but it is not required. A Servlet is nothing but another .java file and all rules that are applicable to standard Java classes are applicable to them. Note: Even if you write a constructor in a servlet, it will not get executed.


You only need a constructor if the default constructor will not suffice. Often times, it is useful to have a constructor that takes common parameters so that you do not have to write additional code. For example, a Point class might have a constructor for Point(int x, int y), which would be a shortcut for assigning x and y independently. Other classes may not need any default values assigned, and for this, it is acceptable to just use the default constructor. Finally, some classes are virtual, static, or abstract, and so may not need a constructor because the constructor is unnecessary (static), or may be defined elsewhere (virtual, abstract).


// constructor program to add two number's // program written by SuNiL kUmAr #include<iostream.h> #include<conio.h> class constructor { private: int a,b; public: constructor(int m,int n); int sum(); }; constructor::constructor(int m,int n) { a=m; b=n; } int constructor::sum() { int s; s=a+b; return (s); } int main() { int x,y; clrscr(); cout<<"enter two number's to add \n"; cin>>x>>y; class constructor k (x,y); cout<<"sum of two number's is = "<<k.sum(); getch(); return (0); }


The Situation.. Write a class for soccer game scoring. Provide a constructor that starts each team with a score of zero. Include instance variables to keep the score for both teams. Include a method to add 1 to the score of the first team and a method to add 1 to the score of the second team. Include a method that displays the score of both teams, and the Main method to test, creating two different soccer games. Score points so the first game is 3-2 and the second game is 0-1. Display the scores of each game....can someone solve this??


This is when you overload the constructor so that there isn't just one way you can initialize the class objectAssume you have a class called Foo and you want two different constructorsFoo(int a, int b);Foo(float a, float b);using a method like this can make your classes more dynamic and you don't need to to write a new class to handle different types. Sorry for the lack of Java code, i program in C++ but it you can overload functions and constructors in C++ too.


Every class, including abstract classes, MUST have a constructor. Hard Code that into your brain. But just because a class must have one, doesn't mean the programmer has to type it. A constructor looks like this: class Car { Car() { } // The constructor for the Car class } You notice anything missing in the declaration above? There's no return type! Two key points to remember about constructors are that they have no return type and their names must exactly match the class name. Typically, constructors are used to initialize instance variable state, as follows: class Car { int size; String name; Car(String name, int size) { this.name = name; this.size = size; } } In the preceding code example, the Car class does not have a no-arg constructor. That means the following will fail to compile: Car f = new Car(); // Won't compile, no matching constructor but the following will compile: Car f = new Car("Ford", 43); // No problem. Arguments match // the Car constructor. So it's very common for a class to have a no-arg constructor, regardless of how many other overloaded constructors are in the class (constructors can be overloaded just like methods). You can't always make that work for your classes; occasionally you have a class where it makes no sense to create an instance without supplying information to the constructor. A java.awt.Color object, for example, can't be created by calling a no-arg constructor, because that would be like saying to the JVM, "Make me a new Color object, and I really don't care what color it is...." Do you seriously want the JVM making your color choices?


There is no difference with method declaration and implementation between abstract and non-abstract classes. You do the exact same thing when writing a concrete method in either an abstract or non-abstract class.


Mark a class as MustInherit and at least one method as MustOverride.


By default every class you write inherently extends the base Object class. This has a basic toString() method which merely returns the name of the class followed by a hex representation of the hash value. By overriding this method, you can return a more meaningful value specific to your class, such as member attributes and their values.


Constructor overloading is similar to method overloading. You can overload constructors by changing the parameter list in the class definition. Here is an example public class Box{ private int height; private int width; private int breadth; // First constructor with no parameters Box(){ height = 0; width = 0; breadth = 0; } // This is the second overloaded constructor Box(int h,int w,int b){ height = h; width = w; breadth = h; } public void display(){ System.out.println("Height: "+height+" Width: "+width+" Breadth: "+breadth); } public static void main(String args[]){ Box obj = new Box(1,2,3); obj.display(); } }


Overriding is a feature in Java where you can override (mask) the features of the parent class in the child class. Lets say you have a method printName() in the parent class which prints the name of that class. When you extend this class in a child class if you call the method printName() the name of the parent would be displayed. Which you may want to change. If you want to display only the name of the child class then you can write the method printName() in the child class. On invocation the name of the child class would be printed. Tip: If you want to display the name of the parent class somewhere you can invoke it by using super.printName() because once you override that method in the child class you cannot access the parent class method directly.


A constructor is automatically invoked whenever an object is created. The relevance of this is that the programmer of a class can ensure that the object is initialized properly - for example, that certain fields have sensible values - without having to rely on another programmer, who uses the class, who may, or may not, initialize it in the expected way. A constructor may also be used to simplify object creation. For example, say you have a class, Complex, with two data items (fields) called "real" and "imaginary". Without a constructor, to create an object and assign it a value, you would have to write something like: x = new Complex(); x.setReal(5.0); x.setImaginary(2.0); Or perhaps: x = new Complex(); x.setValues(5.0, 2.0); But with a constructor, this can be combined into a single step: x - new Complex(5.0, 2.0);



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