Linked Lists In Java
Nov 27, 2014
I currently don't understand how the node's work.
private static class Node<AnyType>
{
private AnyType data;
private Node<AnyType> next;
public Node(AnyType data, Node<AnyType> next)
{
this.data = data;
this.next = next;
}
}
Why do I make private Node<AnyType> next;And why do I have an inner class of Node for a linked list?I had the same topic in C, but there it was somehow easier than in java. Because there you have pointers.
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Oct 25, 2014
I'm working with Doubly Linked Lists and using Java Generics..
My nodes looks like this:
class DNode<E> {
DNode<E> previous;
DNode<E> next;
E element;
//and all methods inside
}
My list of Nodes looks like this:
class DLL<E>{
private DNode<E> head;
private DNode<E> tail;
private int size;
[code]....
As you can see, as arguments they get "E o"...I need to write a program, which from the main function asks the users how long is the list, and after they type it's length, I ask them to start typing the elements (integers)...and this is how my main method is written, but I can't seem to make it work, specialy when I call the "insLast" method,I guess it's because the arguments i'm giving to the function...how to read the elements and write them into the list?
public static void main(String[] args) throws IOException {
DLL<Integer> lista=new DLL<Integer>();
BufferedReader stdin = new BufferedReader(new InputStreamReader(System.in));
String s = stdin.readLine();
int N = Integer.parseInt(s);
s = stdin.readLine();
String[] pomniza = s.split(" ");
for (int i = 0; i < N; i++) {
lista.instLast(Integer.parseInt(pomniza[i]));
}
}
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Apr 27, 2014
Write a Java function Sum2List that takes two lists L1 and L2 of the same size and returns list L that contains the sum of data inside the corresponding nodes of lists L1 and L2.
ex: L1 = {1,2,3}
L2 = {4,5,6}
L = {5,7,9}
I do not know how to iterate through two different lists >>
public LinkedList Sum2List(LinkedList l1, LinkedList l2){
LinkedList l3 = new LinkedList();
ListNode Current1 = L1.getFront();
ListNode Current2 = L2.getFront();
while(Current1 != null){
l3.Add(Current1.getItem() + Current2.getItem());
[Code] .....
This my attempt to write the code , but the dr. side that we have not to use the build in methods ( getNext()...etc)
in the function .
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Mar 10, 2014
I have an XML sheet and my project is top retrieve the required elements from XML sheet. So my format of XML was like follows:
<Class>
<Employees>
<EMPLOYEE>
<ENum> Abc123</ENum>
<Ename> John<?Ename>
<EType>Mathematics</EType>
[Code] ....
I have used unmarshalling concept to retrieve the data elements... I have to check whether the elements satisfy few regulations when compared with data in Database. So, i thought of grouping the employees depending on EType. I have created a Map with linkedlist of employees. Say Map<String, LinkedList<Employe>>EmpMap=new Map<String, LinkedList<Employe>>();
I have already created a class named Employee which has all the setter and getter methods for employee.
Here am going to take Etype(Employee type) as key and linkedlist(list of employees of certain type) as value. How to iterate these linked lists and place them in my Map.
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Jul 19, 2014
Why is this method throwing a null pointer exception when I call it from main?
I'm trying to submit an integer to indicate the number of nodes in a linked list to delete and then delete them headfirst.
public boolean delete(int x){
if (x > count || head == null){
return false;
}else{ while (x>0){
head = head.getPrevious();
[Code] ....
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Feb 13, 2014
I have the following code that supposed to perfrom sorting on the linked list using method sort in order usind node concept of Linked List but seems to give inlogic results. the following code tests only the values lower than the first value but i can't manage to sort the data higher than the first entered value;
/*
* To change this template, choose Tools | Templates
* and open the template in the editor.
*/
import java.util.*;
public class ListNode<T extends Comparable> {
ListNode<T> nextNode;
T data;
public ListNode(T item)
[Code] .....
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Apr 16, 2014
I am creating a chained hash table that uses my own LinkedListclass to handle collisons. Here is where my issue is occuring: I start with an array of LinkedLists, my "hash table", intially set to null. When i wish to add a word, if the desired location is null, I create a new LinkedList, place it in that array index. I then create a new LinkedListNode and set the head of the new LinkedList to the new node.
My issue is occuring here: Whenever I set the head of my new LinkedList to my new LinkedListNode all of my previously created linkedlists also have their head changed to the new node.
My debugger shows that I am truly creating new linkedlists every time. I was afraid each array index was just pointing to a single array, but that is evidently not the issue. Below is all the relevant code
public class SetOfStrings {
private int arraySize;
private LinkedList[] mainArray;
private int totalCount;
//other methods here
public boolean add(String toAdd) {
int hashToAdd = hash(toAdd);
[code]....
SUMMARY: Whenever I set the head of a Linked List to a new node, it changes the head of all my linked lists to point to the same new node
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Oct 29, 2014
Basically, the program is to be able to read information from a file like this;
11111 63.5
22222 59.9
33333 82.4
44444 73.1
55555 77.3
66666 99.5
77777 68.7
88888 53.2
99999 66.8
where the first number is student number and the second is their grade. I need to read this information from a .txt file and dynamically create a new node containing that student's number and mark, and insert it in the correct position in the linked list (in descending order based on grade). So I get that each Node needs to contain two data types, an Int for Student # and a Double for their grade, and I'm pretty sure I've done it correctly with my StudentNode class which can be found in the source code linked above.
But what I don't get it using that class to create Nodes in my main class and then sort them based on their Double grade value WHILE they are being sorted. I just don't understand where to actually put the methods and such that does these things. Apparently I'm supposed to have three classes.
One named StudentNode which is just the node info, which I have done.
The second is called StudentList which is apparently supposed to contain the head of LinkedList and the methods I need? I'm not sure how it ties into StudentNode though.
The third and final is just the main class which I'll use to test it.
Then after all that I need to print out the median mark through a recursive method that isn't allowed to use any loops or call and functions/methods that use loops. The function should return the node in the list which contains the median mark. Secondly, in order to find the median, you need to know how many items in total are in the list. Your recursive function must calculate that number (also recursively); you may not keep track of this count elsewhere your program. Your recursive solution should only examine each node only once, and the depth of the recursion should be equal to the number of nodes in the list.
Here's my current in-progress code.
import java.io.FileNotFoundException;
import java.util.Scanner;
class StudentNode {
private int studentNum;
private double grade;
private StudentNode next;
[Code] .....
I'm pretty sure the StudentNode class is fine, it's the StudentList class that I'm not sure about. I'm not sure how to add nodes since there isn't a getNext() method in the StudentList class.
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Oct 25, 2014
I'm not sure if my understanding of PriorityQueues is correct, so I'm trying to check if my reasoning is valid. I'm supposed to compare the Big-O for arrays and linked lists for the following instructions:
Insert 100 objects having the priorities 1, 2, 3, ... , 99, 100
Big-O for Array: __________
Big-O for Linked List: ___________
Insert 100 objects having the priorities 100, 99, 98, ... , 2, 1
Big-O for Array: __________
Big-O for Linked List(Assume no tail reference): ___________
If my understanding is correct, priority queues take in items randomly with no particular order, but they are removed according to the priority of each element. If what I've said is true, wouldn't that mean that inserting any number of objects would be O(1) for both linked lists and arrays? If the PriorityQueue has no particular order, then wouldnt each add() simply insert something to the next array index/linked list node?
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May 6, 2015
I am trying to implement product method below which returns the set representing the Cartesian product of the current set and a given set (the Cartesian product contains all ordered pairs (a, b) where a belongs to the current set, and b belongs to the given set). The product should be a ListSet <Tuple<E>> object where each ordered pair is a Tuple element. (I have a Tuple class which implements an ordered tuple)
What am I trying to do in the product method : Make 2 for loop and inside the for loop make an array of <E> then set the 2 elements of the tuple then again set tuple and add it to arrayList. how to set 2 elements of the tuple and set tuple ??
public class ListSet<E> implements Iterable<E>{
SinglyLinkedList<E> sl;
public ListSet(){
sl = new SinglyLinkedList<E>();
[code]....
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Nov 2, 2014
How to go through each link item in both lists, and directly link them into the new list in order without using insert()
class Link {
public long dData; // data item
public Link next; // next link in list
// -------------------------------------------------------------
public Link(long dd) // constructor
{ dData = dd; }
// -------------------------------------------------------------
public void displayLink() // display this link
{ System.out.print(dData + " "); }
} // end class Link
[Code] ......
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Feb 9, 2014
I have two JComboBox the first contains a list of patients, the second a list of antibiotics I want to make a button when I chose an antibiotic and a patient they will be added in my database (sql server)
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Oct 9, 2014
I am trying to write a code that allows you to input 2 lists and it tells you if they are identical or not. However, when I enter my fist list I can only enter two values and then it asks for the next list. How would I fix this to allow me to enter more than two values?
Also, If the second list is different it has me enter more values that list one.
public static void main(String[] args) {
Scanner input = new Scanner(System.in);
// Enter values for list1
System.out.print("Enter list1: ");
int size1 = input.nextInt();
int[] list1 = new int[size1];
for (int i = 0; i < list1.length; i++)
list1[i] = input.nextInt();
// Enter values for list2
System.out.print("Enter list 2: ");
[code]...
My output looks like this:
Enter list1: 1
2
Enter list 2: 2
3
2
Two lists are not identical
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Apr 12, 2014
I am creating a recursive method to reverse a linked list in java. It works the first time when I call it, but I want it to work where I call it a second time and it reverses it to the original state. How can I get that to work with this implementation?
public void reverseList() {
System.out.printf("%-16s%-3s%n", "Name", "Score");
System.out.println("--------------- -----");
reverseList(first);
} public void reverseList(Node aNode) {
if (aNode != null) {
reverseList(aNode.next);
System.out.printf("%-15s%6s%n" , aNode.name , aNode.score);
}
}
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Apr 6, 2014
I am creating a josephus java program with a circular linked list.This is what the methods are suppose to do
a. size(): Returns the number of items in the list.
b. isEmpty(): Returns true if the list is empty and false otherwise
c. advance(): Moves the cursor from the current position to the next item. If the cursor is at the end (tail) of this list, calling advance() should make the cursor refer to the first element in the list. If the list is empty, this operation should have no effect.
d. getCurrent(): Return the String value in the node referenced by the cursor unless the CircularLL is empty in which case write an error message to System.err.
e. add(String data): Adds a new item to the list by creating a newNode and linking it to the end of the circular linked list. The last node should point to the new node and then you should make lastNodeInserted point to new node as well.) Please note that a circular linked list is always circular. The last node should point to the beginning node. When there is only one node in a CircularLL, its next should point to itself. This method updates currNode when the first node is added, and always updates lastNodeInserted and numNodes. Take care when adding the first node this is a special case and should be handled differently.
f. remove(): If the list is empty, write an error message to System.err indicating that an attempt was made to remove from an empty queue and return null. Assuming the list is't empty, this method removes the node currently referenced by the cursor, reassigns the cursor to point to the next node in the list, and returns the String value stored in that node. To keep the list linked, you'll need to locate the previous node to the one youre removing and connect its next to the node which follows the one youre removing. Create a local Node variable (prev) to find it. Consider and handle the special case when there is only one node and youre removing it. And make sure to update lastNodeInserted whenever you remove the node that it is pointing to.
g. toString(): This should return a String representation of the circular linked list, with the first value displayed being the data of the first node added (not the data in the last node).
public class CircularLL {
private class Node {
String data;
Node next;
public Node(String data) {
this.data = data;
this.next = null;
[code].....
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Dec 11, 2014
I've playing around with linked lists and methods for sorting. So far I've tested the iterative sort, insertion sort, quick sort and they all worked perfectly. Now, I am trying to implement merge sort that would take a linked list of jobs and sort them according to their priority. I found a few solutions on the web, of which I am trying to implemented this one: LeetCode.
My system is a simple one, I do have a linked list of print jobs, each of which has the priority. The following code should sort my print queue and return the link node of the first sorted element. Here's the code.
//defining a job that has priority
public class Job {
private int priority;
[Code]....
The problem I've been trying to solve is that I am getting the stack overflow at line
ListNode<T> h1 = mergeSort(left);
meaning that I am getting into a loop somewhere down through the process of breaking the linked list into half, half or halfs and so on.
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Sep 12, 2014
I have the following double linked list and I'm supposed to order it descending (reverse) using the printInReverse() method; since the list orders itself ascending when the numbers are added, how could I order it descending in this method? Here's the code without implementing descending/reversing methods:
package test;
import java.util.Scanner;
public class MyList {
private Scanner userInput;
private Integer selectedOption;
private MyListElement firstElement = null;
private boolean exitRequested = false;
[Code] ....
I tried to declare a previousElement variable but I didn't figure out how I'd do that.
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Jul 27, 2014
I'm trying to build a program that contains the ability to:
(1) insert new node at head,
(2) print out contents of the list in order,
(3) remove first node from head,
(4) remove last node from tail,
(5) find a target value,
(6) give total number of occurrences of a target value, and
(7) give total number of items in list.
The areas I'm struggling with implementing are: (
- remove from tail - I know how to find the final node but I can't quite figure out how to set it to null since its initial type is an integer.
- find a target value - how to make the parameters quite workout so the user can simply input an integer value.
- The solution is probably really simple but I can't figure out how to print out the results of these methods when I call them.
public class Node
{
private int data;
private Node link;
// Node Constructor 1
public Node()
{
data = 0;
link = null;
[code]....
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May 12, 2015
Write a java program to store employee information in a linked list, the program should implement the following functions:
The program should display the list of functions, and ask the user to enter the number of function that he/she wants to do, then perform the function as it is required in the previous table.
import java.util.*;
public class Employee {
Scanner in = new Scanner(System.in);
String Name;
String Address;
String Department;
int ID;
int Salary;
[code]....
this is my out put
Please choose a number:
1-Add a new employee
2-Update employee's info
3-Remove employee's info
4-Exit
1
Enter name:
Enter address:
2
Enter department:
3
Enter ID:
4
Enter salary:
now:
1- why are not my adding coming out in the output only the Enter name & Enter address ??
2- how can I add names and ID's and information to test that program
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Aug 6, 2014
public void myFunc(MyNode n, ArrayList<MyNode> path) {
boolean hasChildren = false;
path.add(n);
int index = path.indexOf(n);
ArrayList<MyNode> statefulPath = new ArrayList<MyNode>();
[Code] ....
I have similar code that I stepped through in a debugger. After running the code I found that it built the desired tree, in this case a root node H with left child L and right child P. I want list of lists to contain all paths from root to leaf. I expected [H, L] and [H, P]. I discovered that statefulPath is not stateful; after a recursive stack frame pops, statefulPath still contains n! But that stack frame just popped! I expected to see statefulPath be [H] in the debugger and it was [H, L]! So I later have a list [H,L,P] which I don't want. How do I make the statefulPath list I want for my algorithm?
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Mar 25, 2015
List list1 = query1.list();
List list2 = query2.list();
for (Iterator itr = list1.iterator(); itr.hasNext();) {
Object[] row = (Object[]) itr.next();
}
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Jun 1, 2014
I have big problem with mergesort in Java. I can't figure out why it do not works. I need write it on lists using Comparable. Here is piece of code:
Java Code:
class MergeSort{
Comparator _comparator;
List lista = new ArrayList<>();
List list_temp = new ArrayList<>();
MergeSort(Comparator comparator){
[Code] ....
I have tried everything, still no results. It's return list with random placed numbers.
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Dec 6, 2014
What is going on here in the main class is a zoo that requires information to be read from and saved to a .txt file. I have made three arrayLists for each .txt file, I am getting errors for illegal start to an expression
import java.io.*;
import java.util.*;
public class ColumbusZoo
{
public static void addHelper(ArrayList<DomesticAnimal> a){
Scanner s = new Scanner(System.in);
System.out.println("What species");
[code].....
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Apr 1, 2014
I am working on a assignment that has to do with array lists, it mainly has to do with adding new elements, telling then where it is it located, if the memory block is empty , ect. so far i have been having problems with my indexOf method which should display the array cell number that a input element E is in, and if it is not in there it should display a -1.
public class MyArrayList<E>
{
private E[] data_store = (E[])new Object[2];
private int sizeofa = 0;
private void resize()// makes the array list bigger if need {
E[] bigspacemaker = (E[])new Object[data_store.length * 2];
for(int x = 0 ; x< sizeofa ; x++)
[Code] ....
Error message:
Exception in thread "main" java.lang.ArrayIndexOutOfBoundsException: 512
at MyArrayList.indexOf(MyArrayList.java:28)
at MyArrayListDemo1.main(MyArrayListDemo1.java:26)
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Feb 5, 2014
A Employee Class where i want to sort there lists one by there salary and one by there name individually as per the requirement ? How we do it?
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Mar 18, 2014
I am familiar with Java but new to JSP. I have a Java Servlet app where user actions are recorded in a SQL Server database amd I now need to quickly put together a JSP front end application to view user actions. I want two drop down boxes to filter the results that will be displayed in a list box. What I need is the first drop down list box to show unique user names that have logged in. I can interrogate the database with the following SQL;
"SELECT DISTINCT(USER_ID) FROM AUDIT_MESSAGE"
Then when a user is selected from the first drop down list box (perhaps some sort of on change event) a second drop down list box shows the logins times of the selected user. Again I can interrogate the database with the following SQL;
SELECT SESSION_ID, EventTIME FROM dbo.AUDIT_MESSAGE
WHERE OPERATION = 'loginResponse' AND RESULTS = 'OK'
AND USER_ID = 'firstdropdownlistselection'
Then finally when a login time is selected in the second drop down list box all events for the selected user while logged in with that login time are displayed in the list box.
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