Constructor In Abstract Class?

Jun 23, 2014

Do we have constructor in abstract class? If we have then what is the use of it?

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Writing Constructor In Abstract Class

Feb 4, 2015

Below Code

abstract class A
{
A(int a, int b)
{
}
}

If we can't create objects for abstract class, what is the need of writing constructor???

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What Are Benefits Of Using Interface Plus Abstract Class Over Just Abstract Class

Oct 8, 2014

What are the benefits of using an Interface plus an abstract class, over just an abstract class?

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What Is Abstract Class

Jun 1, 2014

I am just started to learn java and i am facing trouble learning abstract class.

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When To Use Interface And Abstract Class

Apr 17, 2014

I know whats the interfaces and abstract class and also know that difference between interface and abstract class,but here my doubt is eventhough abstract class more advantage than the interface,then why should we use interfaces and when?

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Reference Of Abstract Class

Aug 29, 2014

I passed my abstract class private final reference to another concrete class and I used abstract class reference as parameter to that concrete class constructor and in my main method and null to that parameter then only that program executes correctly...i placing my code below ..if there is any error tell me where is error occurring then i will check my code...i think my code is right but little bit doubt abstract class concept.

{
}
class concept1 extends concept
{
private final concept parent;
public concept1(concept aparent)
{
parent=aparent;
System.out.println(parent);
}
public static void main(String args[])
{
//concept p=new concept1(null);
concept c=new concept1(null);
}}

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Difference Between Abstract Class And Interface?

May 18, 2011

Difference between Abstract class and Interface??

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Why Can't Create Object Of Abstract Class

Jul 18, 2014

Why we can't create object of abstract class ,when we can create its constructor?

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Temporary Object Of Abstract Class

Feb 21, 2015

I am under the assumption that In the return statement of getReciprocal() method(of the following code), a temporary Number object is created to hold the result of the calculation.

My question is, Number is an abstract class and we are only able to create reference of an abstract class not an object. But then how a temp Number object is created and returned?

class Gen<T extends Number>{
T ob;
Gen(T ob){
this.ob = ob;
}
Number getReciprocal(){ // Number is abstract class

[Code] .....

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Abstract Class Constructors Are Not Recommended

Aug 28, 2014

in abstract class constructors are not recommended since we don't call it directly ...my doubt is below code is right or wrong...

3public abstract class Concept
4{
5 private String id;
6
7 protected Concept( String anId )
8 {
9 if ( anId == null )
10 {
11 throw new NullPointerException( "id must not be null" );
12 }
13
14 id = anId;
15 }

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Create Abstract Auto Class

Jul 23, 2014

I'm learning about abstract classes and I have to create an abstract auto class with make and price of a car, then two classes with a different type of car, and finally a main to use them. Everything seems to work and when I run it it's fine but I do get an error on the main that I'm not using the local variable buick1 and acura1.I'm curious because, while it runs for me, I want to make sure I'm doing it right and don't know of another way to do the output than this. I've put all four classes but the issue is on the last one (5 and 7).

public abstract class Auto
{
protected String makeCar;
protected double priceCar;
public Auto(String newMake)
{
makeCar = newMake;

[code]....

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Can Create Object For Abstract Class

Oct 5, 2014

Animal ob1=new Lion();

Here we create ob1 for Animal class or Lion class.

public abstract class Animal {
public abstract void eat();
public void breathe(){

[Code] ....

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Interface Inside Abstract Class

Jul 8, 2015

What this interface inside that abstract class does. Looking for some examples to how can i use it .... 

public abstract class Expression {
  public abstract String toString();
  public abstract SimpleExpression evaluate();
  public void show() {
  System.out.println(this + " = " + evaluate());

[Code] ....

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Private Variable With Type Of Abstract Class

Oct 10, 2014

I've got an abstract class

public abstract class AbstractClass
{
//stuff
}

And a few classes that inherit from it

public class Class1 extends AbstractClass
{
//stuff
}
public class Class2 extends AbstractClass
{
//stuff
}

within another class I have a private variable with the type of the Abstract class, and within one of the methods I assign an object to the the variable like this:

public class Test
{
private AbstractClass temp;
public testMethod(){
Class1 anObject = new Class1();
temp = anObject;
}
}

Is this legal? Will temp become a Class1 object?

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Pass Private Final Class Object To Another Class Constructor

Aug 28, 2014

can we pass private final class object to another class constructor?

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Declaring Class In Main Class - Constructor Cannot Applied To Given Types

Aug 1, 2014

So i declared a class in main class but it seems there's error when i compile:

constructor xx in class xx cannot applied to given types

This is my java class:

public class trainer extends person{
String classType;
public trainer(String name, String gender, String address, int id, String classType) {
super(name,gender,address,id);
this.classType=classType;

[Code] ....

And this is the way i declared in main class:

trainer tr = new trainer();

And what i want to do is:

tr.toString();

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Performing Method On Instance Inside Abstract Class

Mar 12, 2015

How do I create an instance of a class in a method?

I am a bit rusty whenever I think of instances. I always think of main method and objects when I see instance which gets me confused on what to do when I am not in a main method. The example:

I have a abstract class, School, and inside School I have some methods that must preform some action on an instance. For example, there is a move() method that must move the instance of School. Another method named, personOld(), which returns whether or not an instance of School surpassed some determined age.

How do I do this and create this instance?

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Why Keyword Is Needed Infront Of Abstract Class Methods

Mar 7, 2014

I have a simple classes here one is interface and another one is abstract class when i try to compile them abstract class is givving compilation error.

public interface MyInterface{
public void getName();
public void getName(String s);
}
public class HelloWorld{}
abstract class SampleClass{

[code]....

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Why Super Classes Always Declared As Interfaces And Not Abstract Class

Dec 1, 2014

While reading the design patter book, i got one doubt ,There is a List an interface having sub classes ArrayList, LinkedList etc.,

Q1) My question is Why they declared the List as interface rather than Abstract class?

Q2) i read some site -

List l = new ArrayList(); Why it is GOOD line?
ArrayList l = new ArrayList() ; Why it is BAD line?

Answer required with detailed information for Q1 and Q2.

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Creating New Constructor In Child Class Which Is Not In Parent Class

Feb 7, 2014

I've a parent class with a argument constructor like below(a sample code)

public class Parent {
Parent(String name) {
System.out.println(name);
}
public static void main(String[] args) {
}
}

Also I've child.class which extends Parent.class as shown below,

public class child extends Parent {
child(String name) {
super(name);
}
}

Now, I want create/modify the constructor which is in child, by taking "int i" as an input instead of "String name". How can I do that? Run time I want to execute child constructor not a parent constructor.

Condition is: Without making any changes to the Parent class

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Swing/AWT/SWT :: Error At Class Name - Type JTextField Must Implement Inherited Abstract Method

Oct 27, 2014

This code is directly from Swing: I'm using Eclipse and keep getting an error on line 10 saying :

"The type JTextField must implement the inherited abstract method ActionListener.actionPerformed(ActionEvent)."

import java.awt.FlowLayout;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import javax.swing.JFrame;
import javax.swing.JLabel;
import javax.swing.JTextField;
import javax.swing.SwingUtilities;

[Code] ......

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Constructor In A Class Cannot Be Applied To Given Types

Feb 13, 2015

This code works

public class RedShapeDecorator extends ShapeDecorator {

public RedShapeDecorator(Shape decoratedShape) {
super(decoratedShape);
}

Below results in an error

public class RedShapeDecorator extends ShapeDecorator {

protected Shape decoratedShape;
public RedShapeDecorator(Shape decoratedShape) {

this. decoratedShape=decoratedShape;

}

So I am guessing that if you extend class, you should use super to pass objects?

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Constructor Error When Extending A Class?

Oct 21, 2014

I am writing a program that should take a url and scan the page for any links. It is in the beginning stages, but I ran into an error when I tried to extend a class. There's a lot going on in this code, but the error is caused by the constructor.

Error message at compile time:

"constructor Page in class Page cannot be applied to given types;
{//Constructor
^
required: String
found: no arguments
reason: actual and formal argument lists differ in length".

Here's the code(first my class, then the class I extended)

public class SearchEngine extends Page {
public static Color customGreen = new Color(69, 194, 33);
public static Color customYellow = new Color(232, 166, 12);
public static Color customBlue = new Color(25,97,255);
public static Color customYellowComp = new Color(178,125,0);

[code]...

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Private Variables In Class / Constructor

Jan 7, 2014

When creating a class with a constructor, why does one have to create private variables (attributes) to be used as parameters by the object? The object's parameters will be set to be exactly equal to the private variables (attributes), so what is the point of having the private variables (attributes) Why are both private variables (attributes) and parameters needed when they are set to be equal each other anyway?

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How To Test Default Constructor In Different Class In Java

Nov 5, 2014

How do you test a default constructor in one class and then test it in a different class? This is the code for the Person class which has the default constructor. I'm not sure in the PersonTester class how to access this default constructor and how to test it - what I have so far for the second class is also below.

class Person {
// Data Members
private String name; // The name of this person
private int age; // The age of this person
private char gender; // The gender of this person

[code]...

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Type Inference With Constructor Of Generic Class

Jul 15, 2014

I am following this article : [URL] ....

It is important to note that the inference algorithm uses only invocation arguments, target types, and possibly an obvious expected return type to infer types. The inference algorithm does not use results from later in the program.

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