Casting For CompareTo
Nov 11, 2014
I am trying to compare some items from a generic arraylist with each other, but I keep getting an error stating that I need to cast the values in line 38. However, when I heed the warning and change it to what it wants, I get a warning stating "type safety: Unchecked cast from K to Comparable<K>". Should I ignore this warning or is there a better way to compare the two items? Also, is there another way for me to use compareTo w/o making my class extending/implementing comparable or is that the only way?Here is what I have:
class WordInfo<K, V extends Comparable <K>> {
private FileReader fr;
private String word;
private ArrayList<K> list;
private BufferedReader br;
private int current = 0;
[code]....
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Feb 24, 2014
i have this problem with my code. it need to put three names in alphabetical order that are entered from the user. then output the alphabetical result. the program compiles but when you put in different names there are not alphabeticals. i think only the first if works good.
import javax.swing.JOptionPane;
public class Sort
{
public static void main(String[] args)
{
String name1;
String name2;
String name3;
[code]...
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Jan 8, 2015
Lets suppose that I pass to the sort method a list of 2 objects of the same class (which implements Comparable interface). I read (in head first java) that one object is compared relative to another with one object calling the CompareTo() while the other object being passed as a parameter to the same method. Now am I safe in assuming that the first object in the list calls the method with the second object being passed as a parameter.And also how does the CompareTo() work if there are more than 2 elements in the list. Which objcet calls the method and which is passed as a parameter?
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Jul 16, 2014
My instructor gave me this code to use as my Array sort. I can not get this to work. I do not get any compile errors, the code just does not do anything.
Java Code:
package inventoryprogram4;
import java.util.Scanner;
public class Inventoryprogram4
{
static GUI mainGUI = new GUI();
static String outText = "";
[Code] .....
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Oct 31, 2014
Here is my code:
/*
* Implement the Comparable interface on objects of type Order.
* Compare orderId, then productId. The lesser orderId should come first. If the orderIds match, then the lesser productId should come first.
*/
@Override
public int compareTo(Order ord) {
// TODO Auto-generated method stub
if(orderId > ord.orderId){
return 1;
[Code] ....
Here is the output:
Actual: 0
Expected: -1
Actual: -1
Expected: -1
Actual: 1
Expected: 1
Actual: 1
Expected: 1
Actual: 0
Expected: 0
Actual: 0
Expected: 0
In short, the "Actual" is what my code produces and the "Expected" is what it is supposed to produce. As you can see, only the first one is mismatching... I'll admit, the comment section above the method is confusing and I wasn't exactly sure what it wants me to do, but I thought I figured it out. I just don't see how 5/6 of these tests can work and the 6th one not.
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Jan 29, 2014
I have studied that Generics are used to shift the Class Cast Exception into Compile time errors , So that we get errors at compile time error and we do correct them before executing ,but Here is a program in which i am getting Class Cast Exception
class Animal
{
}
class Dog extends Animal
{
}
class Cat extends Animal
[code]..
Getting Exception at line no 29 which i know why it occurs but just wanna ask that isn't it should be caught at compile time According to Generics ?
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Aug 21, 2014
The following code snippet will print 'true'.
short s = Short.MAX_VALUE;
char c = s;
System.out.println( c == Short.MAX_VALUE);
Correct Option is : B
A. True
B. False
Explanation:
This will not compile because a short VARIABLE can NEVER be assigned to a char without explicit casting. A short CONSTANT can be assigned to a char only if the value fits into a char.
short s = 1; byte b = s; => this will also not compile because although value is small enough to be held by a byte but the Right Hand Side i.e. s is a variable and not a constant. final short s = 1; byte b = s; => This is fine because s is a constant and the value fits into a byte. final short s = 200; byte b = s; => This is invalid because although s is a constant but the value does not fit into a byte. Implicit narrowing occurs only for byte, char, short, and int. Remember that it does not
occur for long, float, or double. So, this will not compile: int i = 129L;The below code compiles fine and contradicts what is said in bold. So what does the bold statement mean then?
Java Code: class BreakTest{
public static void main(String args[])
{
float f=1.0f;
double d=f;
}
} mh_sh_highlight_all('java');
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Jun 16, 2014
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?
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Apr 26, 2015
I've tried implementing the compareTo method in several ways and no luck.. I keep getting errors and now it just says bad operand type for binary operator with the ">" symbol and also the less than. I'm attempting to give an implementation for the compareTo method so it compares the value of the requestDate instance variable of the two objects. if the calling object of request is greater then I have to return ""1" if it's smaller then returns "-1" and if they are the same then returns value of "0"
package librarysystem_phase2;
import java.io.Serializable;
/**
* This class represents a request a member makes to checkout or download an item from the library.
*/
public class Request implements Serializable, Comparable<Request>
[code]....
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Apr 16, 2014
I am getting a NullPointerException at my compareTo statement in this section of my code. Why this is popping up?
public static int findPos(String theArray[], String playerName, int arrayCount)
{
int index;
int pos;
for(index = 0; index < arrayCount; index++) {
while ((index < arrayCount) && (playerName.compareTo(theArray[index]) > 0)) {
index++;
}
}
pos = index;
return pos;
}
Error is also creeping up on the line highlighted in a comment as "THIS LINE", and is linked to the compareTo error above.
while(yesOrNo == 'Y' || yesOrNo == 'y')
{
switch(option)
{
//Add a Player and their Stats to the Array
[Code] ....
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Oct 2, 2014
I have to create a program that uses the Scanner in String input and Output that will enable the user to convert
double -> int
int -> byte
int -> short
int -> hex-string
The output should look something like this:
Syntax: convert <value> <type>
convert 15.5 int~> 16
convert 128 byte~> -128
<type>: int, byte, short, hex, decimal
Syntax: max <type>
max byte~> 127
<type>: int, byte, short
[Code] ....
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Aug 3, 2014
import java.io.IOException;
import java.util.*;
public class Guesser {
public static void main(String[] args) throws IOException {
char[] alphabet = "abcdefghijklmnopqrstuvwxyz1234567890 .,:;'-".toCharArray();
[Code] .....
I'm writing a program which will take a three letter word (for now) and then try to guess the word over and over again until it finds it, then print the word and the amount of tries it took to find it.
The problem: at the moment the program will find the word but not break out of the for loop when it does. I think it doesn't like the char to String conversion somewhere along the line.
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Mar 17, 2014
how to calculate the child's height in float value fixing value where if you choose male the accurate value, but if you choose female the value will be accurate too.
int heightMother, heightFather;
int heightMaleChild, heightFemaleChild;
String gender;
[code]....
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Mar 28, 2014
I am having difficulty with a sorting routine. I believe that the concept is valid (although not necessarily the most efficient), but I keep running into a problem. I am trying to use the compareTo function to identify the relationship between two values in an array, but it seems to have an issue with it being a comparison of two float values.
Java Code:
for (int x = 0; x < 430; x++) {
for (int y = 0; y < 430; y++) {
if (dataArray[y].compareTo(dataArray[y + 1]) > 0); {
tempOpen = dataArray[y];
[Code] ....
It gives the compile error as follows:
File: C:UsersBradDownloadsAssignment 3Calculations.java [line: 157]
Error: Cannot invoke compareTo(float[]) on the array type float[]
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Mar 9, 2014
I have a project where I must sort a collection of songs by a number of fields: year, rank, title and artist. in the project, we must use certain methods and we cannot add others without getting marked down. Here are the specific requirements:
Sorting
The -sortBy option will cause the output to be sorted by a particular field. If this option is specified, the output should be ordered according to the field named. If there are ties, the tied songs should appear in same order in which they were in the input file. If no -sortBy option is specified, the output should maintain the order of the input file.
public void sortYear()
Order the songs in this collection by year (ascending).public void sortRank()
Order the songs in this collection by rank (ascending).public void sortArtist()
Order the songs in this collection lexicographically by artist (ascending, case-insensitive).public void sortTitle()
Order the songs in this collection lexicographically by title (ascending, case-insensitive).
Here is the relevant code:
SongCollection Class
Java Code: import java.io.File;
import java.io.FileNotFoundException;
import java.util.ArrayList;
import java.util.List;
import java.util.Scanner;
import java.util.*;
[code]....
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Oct 17, 2014
why my session not type casting into String? I'm placing that code below where problem arised.
HttpSession hs1=request.getSession(false);
out.println("hi");
String t1=(String)hs1.getAttribute("name");
out.println("hi "+t1);
in my above code first "hi" is printed successfully but next statement arises type cast exception.
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Jul 15, 2014
There is a sentence in JLS 7 which I can't figure it out. It says :
A cast from a type S to a parameterized type T is unchecked unless at least one of the following conditions holds:
-S <: T
-All of the type arguments (§4.5.1) of T are unbounded wildcards
-T <: S and S has no subtype X other than T where the type arguments of X are not contained in the type arguments of T.
Condition one and two I got it. But the number three is really bugging me. I write some code in order to try to understand it.
class G<X>{}
class D<T,U> extends G<T>{}
G<String> g = new G<>();
D<String, Integer> dd = (D<String, Integer>) g;
In Eclipse I got no warning but it shouldn't give one ?
Because g has others subtypes than D<String, Integer> (e.g. D<String, List> , D<String, G>)
Am I missing something about the contained type arguments ?
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Oct 15, 2014
import java.util.*;
public class CommonElements
{
private int comparisons; // number of comparisons made
private Comparable[] arrayToSearch; // current array being traversed
private Comparable[] commonElements = new Comparable[10];
private int arrayPosition = 0; //keeps track of what index to add an element to common at
[Code] ...
I have trying to get this down to the bar minimum. I am trying to cast the desired object array to a array of comparable. This is all required by the assignment.
I am getting a runtime error that I can not perform the desired cast. What do I need to provide the compiler in order to allow for this casting. I can not change the signature of the method however nothing about the class has been specified do I need to implement comparable? Also I don not now what the client is passing so how would I write a generic compareTo method to compare object of unknown types.
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Jun 7, 2013
"Type Casting" .... So the question is "How am I getting a number with two decimal places as output?"
import java.util.Scanner;
public class SalesTax
{
public static void main(String[] args) {
double purchase, tax;
Scanner input = new Scanner(System.in);
System.out.print("Enter purchase amount: ");
purchase = input.nextDouble();
tax = purchase * 0.06;
System.out.println("Sales Tax: $" + (int)(tax * 100) / 100.0); +//this will give two decimal places??+
}
}
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Oct 6, 2014
I'm having trouble with sorting Strings- 3 strings inputted by user, and I would like to output them in alphabetical order. I've used the str.compareToIgnoreCase method, and then I've tried to loop them through a series of if/ else statements. Everything I've been able to find online (including the forums here) has suggested to use the Comparator class, or to put the strings into an array, and sort list- I really would like to stick with just the String class, and its methods .
The program itself works and compiles, but I am getting logic errors that I have been unable to solve. I'm using IntelliJ Idea, and I've ran it through the built in debugger, about 100+ times (not exaggerating, lol) just to see what it's doing in particular scenarios. For instance, I can get c, a, b, to print out as a,b,c correctly, but a,b,c, will print out as b,a,c.
For me this is kind of like a Sudoku puzzle, or a Rubik's cube! Each time I fix one scenario, it breaks another one, so I don't know if there's a(logic) solution to fix all possible scenarios (abc, acb, bac etc... to all print abc) or if possibly I just need more if statements. I've only pasted in the area where I'm having problems (the if statements). I'm a big fan of the "Next Line" syntax.
(Note: please assume the non relevant content- import Scanner class, main method, etc... I didn't want to paste the entire program.)
System.out.println("Enter the first statement: ");
//input.nextLine();
string1 = input.nextLine();
System.out.println("Enter the second statement: ");
string2 = input.nextLine();
System.out.println("Enter the third statement: ");
string3 = input.nextLine();
[Code] ....
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