Winston Gutkowski in one of the threads that one of the advatanges of String being immutable is that its hashcode could be cached. How does this work? I read somewhere that each String's hashcode is stored in a private int variable, but I don't understand how it is reused.
View RepliesHow do we cache objects in EJB 2.
My requirement is i need to get data from the database for the first time and retain in cache it throughout the application life.
how a JTable and respective DB table would be updated via directly editing a JTable: After table cell is updated, the setValueAt method of my custom TableModel is called to change the value of the data vector (assume I'm using vectors to store data). setValueAt then calls fireTableCellUpdated which updates the table view, and calls my custom TableModelListener.tableChanged method. Here is where I would write code to update the database.
This means an Update statement is fired each time a cell changes. Sometimes I would like to only send the Update after the entire record has been updated (and a user clicks a Save button).
Does the following code, which gets a class from a remote server, caches the class on the client machine?
URL u = new URL("http://1.2.3.4:80/JavaClasses/MainClass.class");
InputStream input = u.openStream();
DataInputStream data = new DataInputStream(input);
byte classBytes[] = downloadByteCodesFromURL(data);
Class c = defineClass("MainClass", classBytes, 0, classBytes.length);
[Code] .....
When we are caching an object, how to set expire time for that object by using pre defined methods?
View Replies View RelatedIts that very old question regarding hashcode and equals implementation which i am not getting .
import java.util.*;
public class MyElement {
public static void main(String a[]){
HashSet<Price> lhm = new HashSet<Price>();
lhm.add(new Price("Banana", 20));
lhm.add(new Price("Apple", 40));
[Code] .....
In the above program even if i comment out the Hashcode method , i believe it is still taking the memory address values from the native hashcode method of Object class. but the equals override implentation says that i have two insertions which are same . So as per my logic it should not allow the duplicate element to enter.but its not so ...the duplicate element is well inserted without hashcode .
The assignment goes like this...Write a Payroll class that uses the following arrays as fields:
employeeID - An array of seven integers to hold employee identification numbers. The array should be initialized with the following numbers:
5658845452012578951228777541
845127713028507580489
hours - An array of seven integers to hold the number of hours worked by each employee.payRate - An array of seven doubles to hold each employee's hourly pay rate.wages - An array of seven doubles to hold each employee's gross wages.The class should relate the data in each array through the subscripts.
For example, the number in element 0 of the hours array should be the number of hours worked by the employee whose identification number is stored in element 0 of the employeeID array. That same employee's pay rate should be stored in element 0 of the payRate array. In addition to the appropriate accessor and mutator methods, the class should have a method that accepts an employee's identification number as an argument and returns the gross pay for that employee.Demonstrate the class in a complete program that displays each employee number and asks the user to enter that employee's hours and pay rate. It should then display each employee's identification number and gross wages.Input Validation: Do not accept negative values for hours or numbers less than 6.0 for a pay rate.
My problem with this program is that everytime I try to print the employee ID's or the wages, I get hashcode or something like it (#[I1a77cdc or something like that). I tried using the toString method, but it lists all of the values, when I'm trying to display one at a time. Here is the code for the class:
// moduleArray class
public class moduleArray {
final int NUM_EMPLOYEES = 7;
int[] employeeID = {5658845, 4520125, 7895122, 8777541, 8451277, 1302850, 7580489};
int[] hours = new int[NUM_EMPLOYEES];
[code]...
This is the demo program to list the ID's. I've been messing with it for some time, and right now I just want it to display values.
import java.util.Scanner;
public class moduleArrayDemo {
public static void main(String[] args) {
final int NUM_EMPLOYEES = 7;
int[] ID = new int[NUM_EMPLOYEES];
[code]...
I am studying Serialization from the SCJP 6 Kathy Sierra book. I came across this code snippet.
public class Cat implements Serializable {
public static void main(String[] args) {
Cat c = new Cat();
try {
FileOutputStream fs = new FileOutputStream("testSer.ser");
ObjectOutputStream os = new ObjectOutputStream(fs);
os.writeObject(c);
[code]....
The output is as follows.
files.Cat@4d43691d
files.Cat@7f39ebdb
1) Why are the two hashcodes different?
2) Serialization is supposed to make and identical copy of any object and all its instance variables. So, if the hashcodes are different, are these objects located in different locations in heap?
I'm trying to make a method that creates objects of a parameterized type randomly, but also to store the hashCode of different objects created and if at any time the percentage of different objects is less than 50% throw an exception.
This last part is where I've gotten stuck. I have created a population property where I store the different hashCodes and update it in the method adding the new hashCode from the new object. But I don't know how to do for to know if the percentage of different objects is less than 50%.
package fp.tipos.apps;
import java.util.ArrayList;
import java.util.Calendar;
import java.util.GregorianCalendar;
import java.util.List;
import java.util.Random;
public class FactoriaApps {
[Code] .....
I read this tutorial about overriding equal and hashcode method. [URL] ....
I understand how to override equal method, by overriding it, We can custom our compare. I also understand How to override hashcode, To make custom hash.
But still I can not understand why we do it? why if equal method override, we must override hashcode method too?If we don't what is the problem?
To honor the above contract we should always override hashCode() method whenever we override equals() method. If not, what will happen? If we use hashtables in our application, it will not behave as expected. As the hashCode is used in determining the equality of values stored, it will not return the right corresponding value for a key.
Is it the right reason in order to override:
Because when we customize equal method so it focus on special variables,We must change the hash code too in order to match with it, so hashcode also focus on those special variable.
I want to extend hashCode method in my class. As we know that hashCode is generating with 32 bit. Now I wanna generate 64-bit hashCode for user given Input.. Input may be string or Integer.
Please let me know.. take me out from this problem..
MY code follows like this...
package hash_table;
public class Hash_table
{
private int num;
private String data;
public boolean equals(Object obj)
{
if(this == obj)
[Code]...
Here is my code the whole program is working correctly but the Boolean equals and the has code and it is a requirement for the assignment. Why it is not working.
I know there are issues with the code I am new with java and was struggling so I have to clean my code up before I submit the assignment but for right now I have the out put the way I want it except the Boolean and hash code methods always output that the rectangles aren't equal even when I know they are and it outputs the not equal statement twice??
import java.awt.Color;
import java.awt.Dimension;
import java.awt.FlowLayout;
import java.awt.Graphics;
import java.awt.Rectangle;
import java.util.Scanner;
[Code] ....
The keys in a HashMap and the values in a Set must all be unique, but this can be circumvented when using custom objects in a HashMap and Set, because the compiler has no way to determine if the objects are equal or not, as shown in the example below:
Java Code:
import java.util.LinkedHashMap;
import java.util.Map;
public class HashCodeEquals {
public void run(){
Person p1 = new Person(1, "John");
Person p2 = new Person(2, "Matt");
Person p3 = new Person(1, "John");
[code]....
Obviously the equals method is needed because that compares the two objects. But why is the hashCode method needed?
I am trying to implement the following example to override the equality and hashCode method if the class has reference type member. I do get the expected result "true" for equal and "false" for non-equal objects. But the print statement in the Circle's equal method is not executed when the objects values are not equal. I don't know what i am missing, though i get the equality result "false" as expected for non equal objects.
class Point{
private int x, y;
Point (int x, int y) {
this.x =x;
this.y = y;
[code]....
How can I write a method that takes a string with duplicates letters and returns the same string which does not contain duplicates. For example, if you pass it radar, it will return rad. Also i would like to know how can I Write a method that takes as parameters the secret word and the good guesses and returns a string that is the secretword but has dashes in the places where the player has not yet guessed that letter. For example, if the secret word is radar and the player has already guessed the good guesses letters r and d, the method will return r-d-r.
View Replies View RelatedI am currently trying to make a calculator in Java. I want to use the String split method to tokenize the string of characters inputted. I thought I was using the String split method wrongly, because I had surrounded the characters I wanted to delimit with square brackets. However, when I removed the square brackets, the code threw an exception when I pressed the equal button. The exception was a PatternSyntaxException exception. Am I using the String split method wrongly? And why is the exception thrown? Here is my code:
import javax.swing.*;//import the packages needed for gui
import java.awt.*;
import java.awt.event.*;
import java.util.Arrays;
import java.util.List;
import static java.lang.Math.*;
public class CalculatorCopy {
public static void main(String[] args) {
[Code] .....
i am trying to write a class method which will take in a string and returns a string which is the reversed version of that string. it compiles fine but when i try to run it it states Main method not found in class StringReverse,please define the main method as public static void main(String[]args). I am new to java and cannot figure out
import javax.swing.JOptionPane;
public class StringReverse {
public String reverseString(String str){
JOptionPane.showInputDialog(null,"Please enter word");
char c = str.charAt(str.length()-1);
if(str.length() == 1) return Character.toString(c);
return c + reverseString(str.substring(0,str.length()-1));}}
I'm having trouble with the last few lines of the code. It's supposed to take a replacement string entered by the user and print out the new string. For some reason it's now allowing me to enter a replacement string
import java.util.Scanner;
public class Project02 {
public static void main(String[] args) {
Scanner keyboard = new Scanner(System.in);
System.out.print("Enter a long string: ");
String lString = keyboard.nextLine();
[Code] ....
Output:
Enter a long string: the quick brown fox jumped over the lazy dog
Enter a substring: jumped
Length of your string: 44
Length of your substring: 6
Starting position of your substring in string: 20
String before your substring: the quick brown fox
String after your substring: over the lazy dog
Enter a position between 0 and 43: 18
The character at position 18 is x
Enter a replacement string: Your new string is: the quick brown fox over the lazy dog <------ isn't taking user input
I have a method for a button so when a user inputs something it then will get the string value and check it against the string value within the properties file to see if it exists.
The properties file is called GitCommands.properties that contains -- > key = value <-- in it
I realised I have not used it correctly hence why I keep getting errors - I am lost on how to use it, I think perhaps that may be the issue here? I need to reference the file but I am doing it wrong? When I do use that piece of code I get null pointer exception too...
textFieldSearch.getText().equals(GitCommands.keys());
This is my button:
JButton btnSearch = new JButton("Search");
btnSearch.addActionListener(new ActionListener() {
public void actionPerformed(ActionEvent e) {
FindSelectedKey();
[code] .....
I understand I am missing my piece of code where it states "//determine whether the string is equal to the property file key string" I understand the logic fine but not actually coding it.
I am trying to split a string based on length(example length 5) of the string. But I am having a issues with this substring(start, end) method. I get all substring which are of length 5. But if the last substring is less than 5 then I am not getting that last substring. But I need the last substring even if it is less than 5.
String s = "fjdjfdfjgffgjhfjghfjkhjhjh";
String spLine;
for(int i=0; i<s.length(); i=i+5){
spLine = s.substring(i, (5+i));
}
>
Code a Java method that accepts a String array and a String. The method should return true if the string can be found as an element of the array and false otherwise. Test your method by calling it from the main method which supplies its two parameters (no user input required). Use an array initialiser list to initialise the array you pass. Test thoroughly.
public class test {
public static void main(String[] args) {
Printhelloworld();
String[] verbs = {"go", "do", "some", "homework"};
printArrays(verbs);
[Code] .....
I'm having trouble to compare two string from my LinkedList. I took me 2 days now trying figure out how to compare the current string to previous string in the linkedlist. Here is my code.
public int compareTo(LinkedListNode n){
//Compare two string
String myHead = data.toLowerCase();
String comparableHead = data.toLowerCase();
return (myHead.compareTo(comparableHead));
}
How do I compare a String to each element of a string array?
For example:
int headscount = 0;
if (coins[i].equals("heads")){
headscount++;
System.out.println("b" + headscount);
}
This doesn't give me the right value because the IDE says that equals() is an incompatible type. I also tried changing the "heads" to an variable, but the results remains the same.
I would prefer using an Array!
So I'm creating a class which when given three inputs uses them as sides of a triangle and tells ther user what type of triangle it is, or if the input is invalid, tells them why it is invalid. I'm readin the input as a string and then trying to split it into a string array, from there checking to see if it has 3 elements.. in which the data is good at that point, and then converting them to ints and checking to see if they're negative ansd finally checking to see if they can work as sides of a triangle ie a+b >c, a+c >b , b+c >a.
I'm trying to split it into an array of strings but am getting an error, and can't seem to figure out why as this should be working from what I've read of the string.split method online.
import java.util.*;
public class TriangleTest{
private int sideA;
private int sideB;
private int sideC;
public static void main(String[] args){
TriangleTest triangle = new TriangleTest("3 4 5");
[Code] ....
The output reads [Ljava.lang.String;@15db9742
I've a problem in encoding a URL string.
I know to encode a string we use,
URLEncoder.encode(stringname,"UTF-8");
But when I use this I'm getting an error telling that the encode method will accept only 1 String argument.
I have a string value returned from a background tool that will range from 0 to possibly terabytes as a full number. I want to format that number to use commas and to reduce the character count using an appropriate size modifier (KiB, MiB, GiB, etc). I've tried converting the string number to a Double value using Double.parseDouble() and then performing the math based on the size of the value with this code:
Double dblConversionSize;
String stCinvertedSize;
dblConversionSize = Double.parseDouble(theValue);
if (dblConversionSize > (1024 * 1024 * 1024))
stConvertedSize = String.format("%,.000d", dblConversionSize / 1024 / 1024 / 1024) + " TiB";
...
I've also tried using
String.valueOf(dblConversionSize / 1024 / 1024 / 1024) + " TiB";
However, the formatting is failing and I'm either getting a format exception or the result is displayed as a number with no decimal component.