I am not getting the concept of interfaces.I know they are used to implement multiple inheritances.I also know the example that we create an interface car with certain methods so that a class like bmw which implements the car interface has to implement these methods.But I don't know how interfaces come handy?I don't know the meaning of a class calls a method using an interface?(i know that an interface can not be instantiated).
View RepliesI am having a hard time trying to understand interface concept.
-what is an interface?
-What the use of an interface?
-what does implement or to implement means?
-What does implementation means?
I use Jade an I'm able to send messages. Now I try to send a Message with not only integers or strings as content but with another concept as content. Here I want to send a Message of the Media, which contains any number of Trackdata.(I left out the import and other blabla stuff cause i is working)
add(new ConceptSchema(MEDIAINFO), Mediainfo.class);
add(new ConceptSchema(TRACKDATA), Trackdata.class);
//Mediainfo
cs = (ConceptSchema) getSchema(MEDIAINFO);
cs.add(CURRENTTRACK, (PrimitiveSchema) getSchema(BasicOntology.INTEGER), ObjectSchema.MANDATORY);
cs.add(TRACKINFOS, (ConceptSchema) getSchema(TRACKDATA), 1 , ObjectSchema.UNLIMITED);
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what does inner class do
View Replies View RelatedI know that static method cannot use non-static methods .Then how the following code works ,where main method is static and this main method calls go() method which is a non-static method .
import javax.swing.*;
import java.awt.event.*;
public class SimpleGuib implements ActionListener {
JButton button;
public static void main(String[] args) {
SimpleGuib gui = new SimpleGuib() ;
gui.go() ;
[code]....
I am having some difficulties grasping the concept of throwing your own exceptions. How do I get this to repeatedly ask the user to enter a valid value for hours. Also i am having difficulties in the method with using the throw new InvalidHrExcep("That value is invalid"); i cannot get this to work.
public class exceptionProgram {
static Scanner console = new Scanner(System.in);
public static void main(String[] args) throws InvalidHrExcep
{
int day=0;
int month = 0;
int year=0;
int hours=0;
int minutes=0;
int seconds=0;
[code]...
Any brief introduction about session in java....
View Replies View RelatedPrompt: Write a class encapsulating the concept of a circle, assuming a circle has the following attributes: a Point representing the center of the circle, and the radius of the circle, and integer.
Include a constructor, the accessors and mutators, and methods toString and equals.
Also include methods returning the perimeter ( 2 x ๐ x ๐ ) and area ( ๐ x ๐^2) of the circle.
Write a client (application) class to test all the methods in your class. I started out trying to thing how to do this and I mapped out a certain idea but do not know how to incorporate the point represent the center of the circle. I am not sure how to proceed further..
import java.awt.*;
public class Circle {
ย public static void main(String[] args) {
ย
final double PI = 3.14;
int x,y, radius = 4;
double area;
double perimeter;
ย
[Code] ...
Below code gets printed as output?
public interface I1 {
public void method();
}
public interface I2 {
public void method();
}
public interface I3 extends I2, I1 {
[Code] ....
I have following code. In this code CSClient is an interface. All methods of CSClient are implementaed in CSClientImpl class. Do I not need CS Client Impl imported in this code ?
How can I call getBranch() of CSClient, which is not implemented in CSClient as " this. getCsClient(). get Branch (new CSVPath(vpath), true);" ? This code works fine without any error in eclipse.
How can a method getBranch(), which is implemented in CSClientImpl class be used in this code without importing CSClientImpl ?
package com.rbc.teamsite.client;
import java.io.File;
import java.io.FileWriter;
import java.io.InputStream;
import java.io.PrintWriter;
import java.text.SimpleDateFormat;
import java.util.ArrayList;
[code]....
Variables defined in interface are public static and final so I was thinking that we should not be able to override the variables in a class thats implementing the interface. But when I am compiling the below class, it compiles fine and gives the correct values. but when I did disp.abhi = 35; it gives a compile error (cannot override final variable)
interface display{
int abhi = 10;
void displayName();
[code]....
what is marker interface?i want to know internal implemenatation and how to write custom marker interface?
View Replies View RelatedI'm having trouble understanding the concept of the interface Connection, and PreparedStatement.
1) The simplest way to put it is how is it possible that this code is creating Connection and PreparedStatement objects? I was always under the impression that interfaces cannot be instantiated, but rather implemented. For example I don't see "public class Prepared implements Connection", or "public class Prepared implements PreparedStatement", But I see "Connection con = null;" and "PreparedStatement pst = null;". So it seems as if the interfaces are being used to create objects called con and pst.
2) If in fact these interfaces are being implemented, where are the method blocks in this code that should have been added in order to fulfill the contract?
package zetcode;
import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.PreparedStatement;
import java.sql.SQLException;
import java.util.logging.Level;
import java.util.logging.Logger;
[code]....
overriding of the compare method.
Here's an example I found:
public class Someone {
String name;
int age;
ArrayList <Someone> listarr = new ArrayList <Someone>();
public Someone(String name1, int age1) {
name = name1;
age = age1;
[code]...
1. In the compare method, what happens when it returns one of the 0, -1, or 1? How does returning such values contribute to the sorting process? How does it take in information (like I know it does through the parameters, but how exactly)?
2. Why do we use the class name for the generics?
The program runs well , it adds the applet but it dosn't update the interface unless I press "_"(Minimize) . To be more clear , the object paints a spring wich goes through 4 stages , it is added to the JFrame but it dosn't uptade until I minimize the frame , that is when it goes to the next stage .
The main class which calls the spring to be added to the frame :
public class principal implements ActionListener ,Runnable{
JTextField field;
JFrame frame;
private class Action implements ActionListener {
public void actionPerformed(ActionEvent event) {
ย frame.repaint();
[Code] .....
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?
View Replies View RelatedI have a snippet here that I'm working with and I have a few questions about it.
button.addActionListener( new ActionListener(){
@Override
public void actionPerformed(ActionEvent ev){
System.out.println("Button Pressed");
}
});
My questions are:
1. How is it possible to use new on ActionListener when ActionListener is an Interface, not a Class. Isn't it illegal to instantiate an Interface?
2. What is going on with the argument to addActionListener? We have the new ActionListener, but we also have a method being defined as well?
I am supposed to implement a custom Map interface and I'm having some trouble with this method:
// 1. From the interface
/**
* Gives an iterator iterating over the key set from the smallest key that is not less than the key provided.
* @param key the key
* @return the iterator
* @throws NullPointerException if key == null
*/
public Iterator<Key> tailIterator(Key key);
[Code] .....
My implementation is wrong according to a JUnit test. Also, to get a full score this method should have a worst case running time of O(log N), which obviously isn't the case now. (My Map implementation is currently based on binary search in an ordered array, keeping a prallel array for the values).
Can an interface extend a class?When I am running the following code it's showing some errors..I have commented them.
class A {
public void methodA() {
System.out.println("Class A methodA");
}
}
interface B extends A //interface expected here {
public void methodA();
[code]....
Can i type cast a interface to ArrayList? suppose there is a interface Named Node.
public interface Node
{
public static final short ELEMENT_NODE=1;
......
.....
}
i want to typecast this interface to ArrayList and fetch all the value.You can use hashtable object class etc.my main moto is to take a value in ArrayList and traverse it.
class Super { static String ID = "QBANK"; }
class Sub extends Super{
static { System.out.print("In Sub"); }
} public class Test{
public static void main(String[] args){
System.out.println(Sub.ID);
}
}
According to me output should be "QBANK" In Sub...BECAUSE sub default constructor will call super() constructor.. below is the definition in jls which i am unable to understand ....
A class or interface type T will be initialized at its first active use, which occurs if:
T is a class and a method actually declared in T (rather than inherited from a superclass) is invoked.
T is a class and a constructor for class T is invoked, or T1 is an array with element type T, and an array of type T1 is created.
A non-constant field declared in T (rather than inherited from a superclass or superinterface) is used or assigned. A constant field is one that is (explicitly or implicitly) both final and static, and that is initialized with the value of a compile-time constant expression . Java specifies that a reference to a constant field must be resolved at compile time to a copy of the compile-time constant value, so uses of such a field are never active uses.
All other uses of a type are passive. A reference to a field is an active use of only the class or interface that actually declares it, even though it might be referred to through the name of a subclass, a subinterface, or a class that implements an interface.
I have the following code that will make linked list and order its elements using self referential objects. but i have the following error:
incompatible types
required: ListNode<T#2>
found: ListNode<T#1>
where T#1,T#2 are type-variables:
T#1 extends Comparable declared in method <T#1>insertInOrder(T#1)
T#2 extends Comparable declared in class OrderedList
import java.util.*;
public class ListNode<T> {
ListNode<T> nextNode;
T data;
public ListNode(T item)
{
this(item, null);
[code]...
i have this code that I need to input into a GUI interface. how to start mixing the two together.
import java.util.Scanner;
import java.util.Date;
import java.text.ParseException;
[Code]....
interface I1{
void show();
void display();
default void put(){
System.out.println("I am from interface I1");
[Code] ....
This code is not working..
I'm working with Libgdx but I have a basic java question. I'm trying to access the overridden methods from and interface in another class via a call but I'm not sure how. This is what I've got so far :
Java Code:
public interface Controller {
public void show ();
}
public class MainActivity extends AndroidApplication implements Controller {
@Override
public void showAd(boolean show) {
System.out.println("TEST");
[Code] ....
Right now this code returns a null pointer at the call.
I need to implement the attached interface ("Locality"). In the attached UML diagram it has a 1 on 1 relationship with the class "Team". I don't know if this can be somehow implemented in Java. Can I create the attribute "team" in the Locality interface and let it be used by the "Town" and "City" classes? Could it be better to implement it as an abstract class instead?
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