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]....
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]....
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]....
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 Replies View Relatedoverriding 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) {
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?
View Replies View RelatedI am making an app that would allow user to buy seat either by Price or Choice (Row and Column). I have Original code where it runs within JAVA IDE I am making same thing but rather in GUI now. I need putting my Buttons, textfield, and area in organize fashion.
I have not explain how these buttons will behave or act but right now putting them in order is priority then I will add action listeners to do the task we intend to do. A Wire Frame of the code looks like this :
Here is NON GUI Code:
import java.util.*;
public class HW06
{
static int[][] seats =new int[][] {
{10, 10, 10, 10, 10, 10, 10, 10, 10, 10},
{10, 10, 10, 10, 10, 10, 10, 10, 10, 10},
{10, 10, 10, 10, 10, 10, 10, 10, 10, 10},
{10, 10, 20, 20, 20, 20, 20, 20, 10, 10},
{10, 10, 20, 20, 20, 20, 20, 20, 10, 10},
{10, 10, 20, 20, 20, 20, 20, 20, 10, 10},
{20, 20, 30, 30, 40, 40, 30, 30, 20, 20},
{20, 30, 30, 40, 50, 50, 40, 30, 30, 20},
{30, 40, 50, 50, 50, 50, 50, 50, 40, 30}
};
static int rowSize, colSize;
static String strChoice;
static Boolean finished=false;
public static void main (String[] args)
[Code] .....
I have a task to create a Java OOP program, I have a class Team which requires a comparable and iterable interface, the only way I know how to do this is either:
public class Team implements Iterable <Mechanic>
or
public class Team implements Comparable <Mechanic>
How do I add both?
I 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'm trying to create a GUI interface in Netbeans that calculates a phone bill.
I created a GUI interface that input:
- Account Name.
- Account Number.
- Number of Minutes the phone was used. (with a textarea so the user input the minutes)
- 2 JRadioButtoms so the user can chose the regular or premium service.
- Amount Due (+10% taxes) (also with a textarea)
- Clear/Enter/Result/Done Buttoms
And I need to output:
- Account Name.
- Account Number.
- Number of Minutes.
- Taxes
- Total Amount Due.
I have a couple of math formulas I have to add them to output the above however I'm new to java so I don't know which code to use.
The math formulas are:
-Regular charges = 20 + ( No. Minutes - 50 ) * 0.20
-Premium charges = 50 + ( No. Minutes - 75 ) * 0.50
-Taxes = ( Regular charges + Premium charges ) * 0.10
-Amount Due = Regular charges + Premium charges + Taxes
I am new to java coding.... When we create anonymous inner class for interface, we get one object for the sublcass of that interface .
In interface there is no constructor then how do we get that object. We know that to create Anonymous inner class we should use one super class constructor.
Whether my understand is correct or not.
I'm looking for a heuristic explanation of how to think of an "interface" as a type. I'm used to think of the 'type' of a class coming form its very definition but I often see casting to an interface which I still feel very uncomfortable about.Other than an interface, are there other unusual ways a 'type' may be referred to?
A second basic question: When you user 'super.f()', will Java go up the calling chain until it finds method 'f' (and report an err if none is found) or does it expect to find 'f' immediately at its very first parent?
Something about implementing Comparator interface isn't very clear to me: overriding the compare method.
Like here for example:
//This sorts a list of objects holding information based on age: the name and the age of the person
public class Person {
String name;
int age;
public Person (String name, int age)
{
this.name = name;
this.age = age;
[Code] ....
What exactly is happening behind the scenes? I don't understand mostly the part where it returns a 0, a 1, or a -1. After it returns one of those values, what really happens next?
For the displaying of the list, is the method toString() being accessed to output the list in the System.out.println statement?
For the generics, why do we use Person?