Collections Interface That Are Ordered?
Jan 22, 2014
I am using this image as a reference to learn the Collection interface better and it seems I must be getting confused with the 'ordered/unordered' types. I thought ordered would mean ordering the objects automatically like a TreeSet using the comparable interface so it could be numerically or alphabetically ordered etc..
Java Code:
public static void main(String[] args) {
Set hashSet = new HashSet();
hashSet.add(1);
hashSet.add(3);
hashSet.add(2);
for (Object o : hashSet){
System.out.print(o + " "); // Prints: 1,2,3 (Unordered but puts the numbers in order....)
[code]...
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Oct 11, 2014
I can't finish my project in my OOP subject,Ordering System Program,but i am finished with the layout and some processes.
I have complication in which i don't know how to code a process that will record all the ordered items.
i have items like [MS1]Taro Milk Tea.. and there's this textbox that will will get the inputted text and get the quantity of it by JOptionPane.
There's this another JOptionPane that will show the order(s) when "Show Order" button is clicked.
My main problem is i can't record additional items if i want to add more . and my variables are all stored in an array.
Any different way of getting the order,quantity,price of it and Sum all of it and Display the Ordered items...
My professor required that we used inheritance so i have 2 subclasses..
import java.awt.*;
import java.awt.event.*;
import javax.swing.*;
public class MilkteaGUI extends JFrame implements ActionListener,WindowListener {
MtGUIProcess mg = new MtGUIProcess();
Label cardNo = new Label("Card Number:");
[Code] ....
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Apr 19, 2014
I am working on an assignment that requires me to implement 2 methods (add() and remove()) and create an inner class (OrderedListNode). I must use data items of type Comparable. The items should be sorted.
I understand what needs to be done, but I am having a difficult time actually writing the code. I added the main method to check to see if my code works, and it doesn't seem like that is even being read.It compiles without error - it only gives a warning of unchecked or unsafe operations.
Code:
package dataStructures;
//This class functions as a linked list, but ensures items are stored in ascending order.
public class OrderedLinkedList {
//return value for unsuccessful searches
private static final OrderedListNode NOT_FOUND = null;
[code]...
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Jul 2, 2014
I am new in Collection, as per my knowledge I have already override the hashCode() and Equals() method in Data class, but when I trying to search the element it is giving "not found". find the bug.
import java.util.*;
public class WordCounter {
public static void main(String args[])
{
HashSet<Data> set=new HashSet<Data>();
set.add(new Data("this",2));
[code]....
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Apr 23, 2014
I am just not sure of some theory in collections, ArrayList and LinkedList maximum capacity depends on the memory allocated to the JVM. But according to few people those list has a maximum capacity of Integer.MAX_VALUE.
According to my experiment, those list has a maximum capacity of Integer.MAX_VALUE since the get method of List accept a parameter of int primitive type (index of element), therefore we can conclude that the maximum capacity of List is equal to Integer.MAX_VALUE.
But what about the Map? get() method of map accepts object(the key of the map). So does it mean that the maximum capacity of Map depends on the memory allocated to our JVM? Or its maximum size is Integer.MAX_VALUE also just like Lists and Arrays? Is there a way to prove it? Is Map designed to hold infinite number of data (disregarding the heap memory space exception)?
And also about Stack, Deque? is it also the same as Map (in terms of maximum capacity)?
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Aug 24, 2014
Today I installed jdk1.8.0_20 on my computer and typed a simple example code in MyEclipse 6.0 IDE, the code listed below:
import java.util.List;
public class Test5
{
public static void main(String[] args)
{
List<String> features = Arrays.asList("Lambdas", "Default Method", "Stream API", "Date and Time API");
features.forEach(n -> System.out.println(n));
}
}
the MyEclipse Editor shows some errors like "Arrays can not be resolved" and "n can not be resolved".
I did use jdk 8 in the build path, but it seems like the jdk 8 did not function properly.
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Feb 24, 2014
The Iteratior provides the functionality of traversing and removal which we can achieve through normal for loop and remove() of the data structure.Then, why do we need Iterator explicitly and as an inner class?
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Oct 30, 2014
When I run my code, I get an error with this line
if(Collections.binsearch(dict, word3) != -1) {
I imported the collections utility and everything. Tell me if you need to see more of the code. The exact error is binsearch is undefined for the type Collections.
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Aug 29, 2014
I have a method that draws a polygon on the screen:
public void poly(List<Point> points) {
//code
}
For the usage of the method, it makes no difference whether points is an array or a List. In fact, switching doesn't even change any of the code in the method since I use a for-each loop. So, my question is, is it a better practice to use a List as an argument, or an array when the method itself doesn't care about which to use?
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Apr 6, 2014
I have searched on internet but did not find something useful. I do not want to use collections. here's what i have written
class ArrayDemo3
{
static void union(int x[], int y[])
{
System.out.println("Union Elements:");
for(int i=0; i<x.length; i++)
{
for(int j=0; j<y.length; j++)
[code]....
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Jul 14, 2014
I am confused with the following function signature in the class java.util.Collections.
static <T> boolean replaceAll(List<T> l, T oldValue, T newValue);
I got the other parts but i could not figure out at all what is the meaning of <T> in the beginning.
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Jun 28, 2014
I am trying to create a java program to sort an array in ascending and descending order. Here is the program I created :
import java.util.Arrays;
import java.util.Collections;
public class ArraySort
{
public static void main(String [] args) {
int [] num = {5,9,1,65,7,8,9};
Arrays.sort(num);
[Code]...
BUT I GET THE FOLLOWING EROOR ON COMPILATION
ArraySort.java:12: error: no suitable method found for reverseOrder(int[])
Arrays.sort(num,Collections.reverseOrder(num));
^
method Collections.<T#1>reverseOrder(Comparator<T#1>) is not applicable
[Code] .....
What's wrong with my program?
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May 11, 2012
I'm doubted regarding the implementation of Collections.binarySearch() method on an ArrayList of objects of a custom class Movie.
Here is the movie class :
public class Movie implements Comparable<Movie> {
String movieName;
String rating;
String director;
String theme;
[Code] .....
The sort/binarySearch in searchByMovieName function is done with natural sorting (and Comparable Interface in Movie class). I mean no comparators involved here. And the comparator that I used for sorting/binarySearching on Movies Director attribute in searchByMovieDirector function is :
public class MovieDirectorComparator implements Comparator<Movie> {
public int compare(Movie movie1, Movie movie2) {
return movie1.getDirector().compareToIgnoreCase(movie2.getDirector());
}
}
But I was not able to implement binarySearch ?? How to implement the binarySearch here. I have google to see only binarySearch working on Arrays or probably ArrayList of String only, but not on ArrayList of custom objects.
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Jan 10, 2014
My friends and me are trying to make online Test taking system. We got a very basic doubt.
We have developed classes and relationship between classes for example : Online Test Taking system will have admin and student class. And Admin will have list of students.. etc.
But question troubled me was: if we use database to store all data for example student details then I can perform all sorts of operations writing sql query and store result in some other database then what is the need of "ArrayList<Student> field in Admin".??
Question is: We can put everything in database and manipulate using database(sql) functions to manipulate it.Then what is the need of Arraylist of anything which is just used to store object details for example student details....??
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Jun 9, 2014
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] ....
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Feb 5, 2014
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]....
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Jan 21, 2015
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]....
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Nov 24, 2014
what is marker interface?i want to know internal implemenatation and how to write custom marker interface?
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Aug 6, 2014
I'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]....
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Aug 22, 2014
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).
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Mar 7, 2014
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?
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Mar 20, 2015
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] .....
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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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Dec 25, 2014
I 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?
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Nov 5, 2014
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).
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May 16, 2014
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]....
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