Getting Error On Equals Method For Objects
Mar 26, 2014
I have to create a class that has two fields. One called length and the other width. I have to make a method that returns the tract area. Similarly, I also have to make a method that indicates whether two objects have the same fields. Here is the code that I have assembled...so far
// create private fields to hold width and length
private double width;
private double length;
[Code].....
My problem is encountered when writing that equals method
if(length.equals(object.length) && width.equals(object.width))
I get an error saying HTML Code: cannot invoke equals(double) on the primitive type double. Meanwhile, I do see, to realize that when I change my fields to capital "Double." The problem disappears; however, in my class I have never dealt with a situation where I have to use capital d in double. In fact, I don't even know what's the difference between Double and double. I do know what double is but not the other one..
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Jan 7, 2014
I am trying to override the equals method for my class TeamMember I have two fields:
private Details details;
private double salary;
Code for override I get an error on salary saying cannot invoke equals (double) on the primitive type (double)
Is their something I am missing/coding wrong?
Java Code:
public boolean equals(Object obj) {
//test exceptional cases
//avoid potential NullPointerException/ClassCastException
if ((obj == null) || (this.getClass() != obj.getClass()))
return false;
TeamMember other = (TeamMember) obj; //cast to a TeamMember object
// compare fields details and salary
return this.details.equals(other.details)
&& this.salary.equals(other.salary);
} mh_sh_highlight_all('java');
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Mar 28, 2014
Create an equals method that takes an object reference and returns true if the given object equals this object.
Hint: You'll need 'instanceof' and cast to a (Geocache)
So far I have:
public boolean equals(Object O){
if(O instanceof Geocache){
Geocache j=(Geocache) O;
if (this.equals(j)) //I know this is wrong... but I can't figure it out
return true;
}
else return false;
}
I think I have it correct up to the casting but I don't understand what I'm suppose to do with the this.equals(). Also I'm getting an error that I'm not returning a boolean... I get this all the time in other problems. I don't get why since I have to instances of returning booleans in this. "returns true if the given object equals this object" makes no sense to me. I assume the given object, in my case, is 'O'. What is 'this' object referring to?
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Oct 2, 2014
For a few days I've been reading about the importance of overriding the equals method. How overriding it actually determines or checks the values stored in the variable. I realize that you can check the values stored in the primitive datatypes with "==", and when you don't override the equals method it acts the same way, right? When used with a reference datatype, "==" or the default equals() method only compares, or sees, if the variable is pointing to the same instance of a class. For some reason, in the examples, what is taking place to actually check the values stored inside the variables.
Here is part of an example (I've added comments for things that are confusing me):
@Override
public boolean equals(Object obj) {
//So we use Object here instead of the class type
// we're overriding this equals method for?
Is this so that we can use it to check different types? (overloading?)
if (obj == this) {
return true;
//Isn't this checking to see if the calling object is the same as the object we're passing to it?
Why doesn't this return false?
}
if (obj == null || obj.getClass() != this.getClass()) {
return false;
}
//How exactly do we check the values stored in each object though?
}
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May 5, 2014
I am attempting to override the equals method from the Object class which checks if two variables point towards the same object. I want the method to check if if the argument being passed in(an object) has the same data(instance variables) as the object that's calling this method. A NullPointerException is being thrown; Here is the code.
package javaapplication5;
import java.text.NumberFormat;
import java.util.Scanner;
import java.lang.Object;
public class Product {
private String product;
private String description;
private double price;
[Code] ....
And here is the stack trace
Exception in thread "main" java.lang.NullPointerException
at javaapplication5.Product.equals(Product.java:42)
at javaapplication5.Product.main(Product.java:24)
Java Result: 1
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Mar 11, 2015
I need to debug the equals method implementation of a class I've made, but I cannot for the life of me get Netbeans' debugger to step into it. I can step into other methods from the class (most of which implement the methods in an interface) that are called in the main method (just like the equals method). I've tried...
-Disabling all the step filters
-Clearing the Netbeans cache
-Moving the call to the equals method out of the if statement it's in and just calling it as its own statement
-placing breakpoints within the equals method as well as on the call to the method
-placing a method breakpoint on the overridden equals method in addition to the other locations
-Using the shift-F7 version of the step into command
I'm using Netbeans 8.0.1 (I don't know if this is the latest version, but the last time I tried to update everything died and I had to completely remove NB and reinstall it) and JDK 8u05 (I think).
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Mar 26, 2015
How would I create a equals method to compare strings in a class that I'm creating. I need to create the method in my class, and then call it in a driver. How would I do this?
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Jan 19, 2014
Write a class encapsulating the concept of a course grade, assuming a course grade has the following attributes: a course name and a letter grade. Include a constructor, the accessor and mutator, and methods toString and equals.Write a client class to test all the methods in your class.
how to test and finish the toString and equals method in this code ?
package labmodule7num57;
import java.util.*;
public class LabModule7Num57 {
// Constructors//
private String name;
private String letterGrade;
public LabModule7Num57 (String name,String letterGrade) {
[code]....
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Apr 18, 2014
I am having trouble using the equals method to return the appropriate value using standard arithmetic.
import java.awt.BorderLayout;
import java.awt.Color;
import java.awt.FlowLayout;
import java.awt.GridLayout;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
[Code] ....
I know that "inText.setText(Integer.toString(secondOperand));" in the code is wrong, I just don't know the right code...
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Nov 22, 2014
I want to loop through each of my objects and call the method for each one. ( polymorphic array )
Error: Constructor Dog in class Dog cannot applied for gives Types
Required String,String
Found: no arguments
Reason actual and formal argument lists differ in length
Java Code:
public class animal {
private String m_type="";
private String m_name="";
public static void main (String[] args) {
[Code] ....
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May 22, 2014
I am little confused about String creation in java.
Doubt 1: How String objects assigned to Pool area:
1. String s="in pool";
2. String s1= new String("not in pool");
How many objects created in statement 1 and 2. According to recent discussion with my colleague, one object created in String pool in case 1. And in case 2, two objects are created, one as literal goes to String pool and other with new() opr goes to Heap.
If above is correct, Ain't we wasting double memory for same object ? Really need clear understanding on this
Doubt 2: How does intern() work: Please see if my below explanation is correct
1. If String literal is already present in String pool , and i create a same string with new operator, reference to object is changed to pool area.
2. If String object is created using new operator and intern is called on it. If same string object is not present in the String Pool, Its moved to String pool and reference to this in Pool is returned.
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Apr 15, 2015
if some of you worked with Unity Game engine (C#) the idea is that game has main loop and once per cycle it call for example Update() method in all objects which implement certain interface.
I would like to repeat such pattern in Java for another another program, not even game related, but I would still need a main loop and event driven behaviour with async call backsSo question is how to implement the fallowing scenario:
Imagine i have interface which implement some methods and one of them is Execute()
I have the main controller class which implement main loop, also multiple other classes which implement the same interface with method Execute(). How can i call this Execute() method on all objects which implement that interface each loop cycle?
Should i keep and track reference of each object which was implemented with this interface and go through inner "for" loop trough each reference and call manually Execute() method in each of them?what if each object implementing interface have to run Execute() method simultaneously? in parallel independent from each other?
Referring back to Unity engine and their Update() method - there is exactly the same situation:you can have multiple objects with script attached, thats script implement interface which has multiple methods and one of them is Update() and once per cycle all objects with that Update() method will be executed in parallel independently
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Apr 4, 2015
This is what I have to create : Write a method that returns the largest object in an array of objects. The method signature is:
public static Object max(java.lang.Comparable[] a)
All the objects are instances of the java.lang.Comparable interface. The order of the objects in the array is determined using the compareTo method.
Write a test program in the main method that creates an array of ten Strings, an array of ten Integers, and an array of ten java.util.Dates, and finds the largest string (i.e. in the alphabetical order), Integer, and Date in the arrays.
Name your java class Max and your java file Max.java.
I am struggling a bit with this code as I am sure you can see, and am at loss. I have never used the compareTo method. Am I doing this right, or on the right track with my code?
public class Max implements Comparable {
public static Object max(java.lang.Comparable[] a) {
java.lang.Comparable tempObj = null;
for (int i = 0; i < a.length; i++) {
if (a[i].compareTo(tempObj) > 0)
[Code] ....
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Jun 14, 2014
Say I have two classes, Author and Book, and I have 2 author objects and 10 book objects. I would like to know how to do two things:
1) Make some sort of connection that makes clear that author X wrote books A, B and F.
2) Call a method from a book object that is connected to an author.
Seeing as I don't know which books will be connected to an author, is there some way to call a method of an object bases on a variable object name? Something like call the getFirstPage() method for every book that is linked to author X?
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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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Sep 30, 2014
having a hard time with my do while loop. for some reason in my else if structure it will break when i using .equals in the do while loop. But if i try doing tmp == "D" || tmp == "d" it will keep looping how can i go about using alternative for .equals?
Here is my code:
do {
Object object = new Object();
System.out.println("For a deposit Enter: D
Withdrawal Enter: W
"
+ "or 'Quit' to exit.");
String tmp = input.next();
if (tmp.equals("D"))
[Code] ....
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May 15, 2014
Its 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 .
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Jan 12, 2015
All I am trying to do is to make a section of code execute if two strings are equal. The two strings are userId and "A001062". When I use the debugger in Eclipse, I can see the value of userId as "A001062" but whatever string comparison I try never evaluates to true. I have tried
userId=="A001602"
userId.equals("A001602")
"A001602.equals(userId)
Assigning A001062 to a string called AAA and comparing userId to AAA
My code is as follows. I have also attached a screen shot from the Eclipse Debugger which makes me think the string comparison should succeed. I never see the debugger execute the print line nor do I see the print line on the JBOSS console.
String userId = StringUtils.trim(nextLine[HR_USER_ID]);
String AAA="A001062";
if (userId.intern().equals(AAA.intern())) {System.out.print("MKP1: " + userId+"-"+managerId);}
if (userId.compareTo("DTS0428")==0) {System.out.print("MKP2: " + userId+"-"+managerId);}
Attached image(s)
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Oct 27, 2014
Okay, I'm having a problem with my LinkedList. When I run the driver program it's telling me that I have no "add" method and I don't know what's going on.
Driver Program:
public class TestLinkedList {
public static void main(String[] args)
{
MyLinkedList<String> L = new MyLinkedList<String>();
L.add("Browns");
L.add("Ravens");
L.add("Steelers");
[code]....
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Mar 27, 2014
(Count positive and negative numbers and compute the average of numbers). Write a program that reads an unspecified number of integers, determines how many positive and negative values have been read, and computes the total and average of the input values (not counting zeros). Your program ends with the input 0. Display the average as a floating-point number.
I moved the different boolean statements around, but I'm not getting the sentinel value to end the run. It continues to let me add integers endlessly. The code I wrote is below:
package exerciseFourOne;
import java.util.Scanner;
public class AverageOfIntergers {
public static void main(String[] args) {
// TODO Auto-generated method stub
int positive = 0; // number of positive integers
int negative = 0; // number of negative integers
int sum = 0; // value of sum of integers
[Code] .....
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Jul 14, 2014
In Java code, write class called Student with the following features:
• a private instance variable int studentNumber that is initialized to zero.
• a private instance variable String firstName;
• a private instance variable String lastName;
• a constructor which takes an integer argument and two String arguments to initializes the three respective data items.
• a public method with signature equals(Student s) . . .
So far this is my code :
public class student {
private int studentnumber = 0;
public student () {
firstname= "forename":
lastname="surname":
public student (integer studentnumber, string firstname, string lastname) {
this.firstname= firstname
this.lastname= lastname:
My question is how do i add the integer in the argument do i have to use int =? and how would i go about doing the public signature equals...
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Mar 25, 2015
Im working on a roman numeral to arabic converter and all I had to do was fill out the conversion method romanToDecimal. But for some reason no matter what number I enter It always says my number is equal to one.
//Quiz 1 EC
import java.util.*;
class Roman {
private String romanNum;
private int decimalNum;
public Roman(){
romanNum = "I";
decimalNum = 1;
[code]....
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Jul 6, 2014
I was reading a book and came across this while loop.
public class Powers {
public static void main (String [] args){
int e;
int result;
for(int i = 0; i < 10; i++){
[Code] .....
This loop presents the following (I'm sure it's not necessary):
2 to the 0 power is 1
2 to the 1 power is 2
2 to the 2 power is 4
2 to the 3 power is 8
2 to the 4 power is 16
2 to the 5 power is 32
2 to the 6 power is 64
2 to the 7 power is 128
2 to the 8 power is 256
2 to the 9 power is 512
I am just having a difficult time understand and grasping this concept. My main issue is result *=2; this is making it very difficult to understand. How is result being replace if it only equals to 1.
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Jan 12, 2015
All I am trying to do is to make a section of code execute if two strings are equal. The two strings are userId and "A001062". When I use the debugger in Eclipse, I can see the value of userId as "A001062" but whatever string comparison I try never evaluates to true. I have tried
userId=="A001602"
userId.equals("A001602")
"A001602.equals(userId)
Assigning A001062 to a string called AAA and comparing userId to AAA
My code is as follows. I have also attached a screen shot from the Eclipse Debugger which makes me think the string comparison should succeed. I never see the debugger execute the print line nor do I see the print line on the JBOSS console.
String userId = StringUtils.trim(nextLine[HR_USER_ID]);
String AAA="A001062";
if (userId.intern().equals(AAA.intern())) {System.out.print("MKP1: " + userId+"-"+managerId);}
if (userId.compareTo("DTS0428")==0) {System.out.print("MKP2: " + userId+"-"+managerId);}
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Apr 13, 2014
I have a JSP page that calls a Java method .. using GlassFish 4.0 it worked just fine, now I'm trying to run it on a new server with Tomcat 6.0 but it keeps giving me this error: "the function result must be used with a prefix when a default namespace is not specified"
Here's my JSP page:
<%@ taglib prefix="c" uri="http://java.sun.com/jsp/jstl/core" %>
......
<jsp:useBean id="diskUtilData" scope="request" class="newpackage.ResultPage" />
.....
<c:forEach var="celldata" items="${diskUtilData.result()}">
[Code].....
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Jan 14, 2014
I am getting these errors with this code, I can not figure why this error is occuring.
what is the issue with this code?
Java Code: package ABC;
import java.util.ArrayList;
import java.util.Scanner;
public class GetInputFromUser {
private ArrayList<String> name = new ArrayList<String>();
[code]....
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