I have a simple loop that checks for any duplicate results,
where studresults holds my results , result is the object result given to the method and r is the current object from the array.
I have been using this method successfully throughout the program although it is not working in this case even though when I debug result and r , are exactly the same does anyone know why this might be? I have tried #Override already as suggested in other answers to no avail.
I am trying to stop duplicated array elements by throwing an exception.
for(Result r : studresults)
{
if(r.equals(result))
{
return false;
}
}
EDIT OK HERE IS THE WHOLE CLASS>
package ams.model;
import java.util.ArrayList;
import java.util.Arrays;
import ams.model.exception.EnrollmentException;
public abstract class AbstractStudent implements Student {
private int studentId;
private String studentName;
private ArrayList<Course> studcourses = new ArrayList<Course>();
private ArrayList<Result> studresults = new ArrayList<Result>();
public AbstractStudent(int studentId, String studentName) {
this.studentId = studentId;
this.studentName = studentName;
}
public String getFullName() {
return studentName;
}
public int getStudentId() {
return studentId;
}
public Result[] getResults() {
Result[] res = studresults.toArray(new Result[0]);
if(res.length > 0 )
{
return res;
}
return null;
}
public boolean addResult(Result result)
{
for(Result r : studresults)
{
if(r.equals(result))
{
return false;
}
}
studresults.add(result);
return true;
}
public void enrollIntoCourse(Course c)
{
//for re-enrollment
if(studcourses.contains(c))
{
studcourses.remove(c);
studresults.clear();
}
studcourses.add(c);
}
public void withdrawFromCourse(Course c) throws EnrollmentException
{
if(studcourses.size() > 0)
{
studcourses.remove(c);
}
else
throw new EnrollmentException();
}
public Course[] getCurrentEnrolment()
{
return studcourses.toArray(new Course[0]);
}
public abstract int calculateCurrentLoad();
public int calculateCareerPoints() {
// TODO Auto-generated method stub
return 0;
}
public String toString()
{
return studentId + ":" + studentName +":" + calculateCurrentLoad();
}
}
Do you already override hashCode method in Result?
If you override equals, you have to override the hashCode method also to allow you return the same hashcode for the similar objects (objects which has the same value but actually different object instances).
I think the default implementation of hashcode will returns different value for a different object instances even though they have the same values.
Instead I converted toString and then compared and it works???
Makes me think there was something slightly unidentical before?
New method
public boolean addResult(Result r)
{
for (Result s : studresults)
{
String sr1 = s.toString();
String sr2 = r.toString();
if(sr1.equals(sr2))
{
return false;
}
}
Related
This is my VO
public class SomeVO {
private String name;
private String usageCount;
private String numberofReturns;
private String trendNumber;
private String nonTrendNumber;
private String trendType;
private String auditType;
public SomeVO(String name,String usageCount,String numberofReturns,String trendNumber,String nonTrendNumber,String trendType,String auditType){
this.name = name;
this.usageCount = usageCount;
this.numberofReturns = numberofReturns;
this.trendNumber = trendNumber;
this.nonTrendNumber = nonTrendNumber;
this.trendType = trendType;
this.auditType = auditType;
}
public String getName() {
return name;
}
public void setName(String name) {
this.name = name;
}
public String getUsageCount() {
return usageCount;
}
public void setUsageCount(String usageCount) {
this.usageCount = usageCount;
}
public String getNumberofReturns() {
return numberofReturns;
}
public void setNumberofReturns(String numberofReturns) {
this.numberofReturns = numberofReturns;
}
public String getTrendNumber() {
return trendNumber;
}
public void setTrendNumber(String trendNumber) {
this.trendNumber = trendNumber;
}
public String getNonTrendNumber() {
return nonTrendNumber;
}
public void setNonTrendNumber(String nonTrendNumber) {
this.nonTrendNumber = nonTrendNumber;
}
public String getTrendType() {
return trendType;
}
public void setTrendType(String trendType) {
this.trendType = trendType;
}
public String getAuditType() {
return auditType;
}
public void setAuditType(String auditType) {
this.auditType = auditType;
}
}
Here is my values
List<SomeVO> myList = new ArrayList<SomeVO>();
SomeVO some = new SomeVO("A","0","0","123","123","Trend","AuditX");
myList.add(some);
some = new SomeVO("B","1","1","234","234","Non trend","AuditX");
myList.add(some);
some = new SomeVO("C","0","2","345","345","Trend","AuditX");
myList.add(some);
some = new SomeVO("D","2","3","546","546","Trend","AuditX");
myList.add(some);
some = new SomeVO("E","2","4","678","678","Non trend","AuditX");
myList.add(some);
some = new SomeVO("F","0","0","123","123","Non trend","AuditA");
myList.add(some);
some = new SomeVO("G","0","0","123","123","Trend","AuditB");
myList.add(some);
Here is my comparator
public String currentAudit = "AuditX";
public class AuditComparator implements Comparator<SomeVO> {
#Override
public int compare(SomeVO o1, SomeVO o2) {
if(currentAudit.equalsIgnoreCase(o1.getAuditType()) && currentAudit.equalsIgnoreCase(o2.getAuditType())) {
int value1 = o2.getUsageCount().compareTo(o1.getUsageCount());
if (value1 == 0) {
int value2 = o1.getNumberofReturns().compareTo(o2.getNumberofReturns());
if(o1.getTrendType().equalsIgnoreCase("Trend") && o2.getTrendType().equalsIgnoreCase("Trend")) {
if (value2 == 0) {
return o1.getTrendNumber().compareTo(o2.getTrendNumber());
} else {
return value2;
}
} else {
if (value2 == 0) {
return o1.getNonTrendNumber().compareTo(o2.getNonTrendNumber());
} else {
return value2;
}
}
}
return value1;
} else {
return 1;
}
}
}
I am trying to sort the VO based on below conditions
First only set of values of currentAudit should be taken in to
consideration i.e., AuditX
a) then it should be sorted with
Usage count in descending order
b) if same usage count found then it
should be sorted with Return count in ascending order
c) if same
return count then it should check for trendType, if trendType
="Trend" then it should sort with Trend number otherwise nonTrend number.
then it should consider rest all auditType's and sorted with
a),b),c) condition as like currentAudit. I tried achieving it and i
ended up with only above comparator. Expected result: D, A, C, E,
F, G. But i get G,F,D,E,B,A,C. Please help me to update the
comparator above.
Your comparator does not meet a simple condition: it is not stateless. A following should always be true: A>B => B<A. In your case, in some scenarios A>B and B>A.
I resolved it by splitting the actual list in to 2 list based on AuditX and rest in another list. Then used below comparator one by one, and then merged in to a result list. Works good.
for(SomeVO some:myList) {
if(some.getAuditType().equalsIgnoreCase("AuditX")) {
auditX.add(some);
} else {
auditY.add(some);
}
}
Collections.sort(auditX, new AuditComparator());
Collections.sort(auditY, new AuditComparator());
public class AuditComparator implements Comparator<SomeVO> {
#Override
public int compare(SomeVO o1, SomeVO o2) {
int value1 = o2.getUsageCount().compareTo(o1.getUsageCount());
if (value1 == 0) {
int value2 = o1.getNumberofReturns().compareTo(o2.getNumberofReturns());
if (value2 == 0) {
return (o1.getTrendType().equalsIgnoreCase("Trend") && o2.getTrendType().equalsIgnoreCase("Trend")) ?
o1.getTrendNumber().compareTo(o2.getTrendNumber()):o1.getNonTrendNumber().compareTo(o2.getNonTrendNumber());
} else {
return value2;
}
}
return value1;
}
The return 1 at the bottom of the comparator makes a bug.
The comparator shall only return 1 if the second element is bigger than the first one, but if they're different, you always return 1, so the very first sorting criteria will be messy.
// a helper for case insensitive comparison
private int compareIgnoreCase(String o1,String o2) {
return o1.toLowercase.compareTo(o2.toLowercase());
}
#Override
public int compare(SomeVO o1, SomeVO o2) {
int result=compareIgnoreCase(o1.getAuditType(),o2.getAuditType());
if (result==0) {
// we need to go to the 2nd criteria
result=o2.getUsageCount().compareTo(o1.getUsageCount());
}
if (result==0) {
// ok, 1st and 2nd criteria was the same, go to the 3rd
result=o1.getNumberofReturns().compareTo(o2.getNumberofReturns());
}
if (result==0) {
// check trends
...
}
return result;
}
I found that this representation of multiple comparison criteria makes the code much easier to follow. We first do the highest priority of comparison, and go on with further comparions if the previous comparisons returned that the two elements are the same (i.e. result is still zero).
In case you need to make a descending sorting at some level, simply put a -, e.g.:
result=-o1.something.compareTo(o2.something)
It is a good idea to have only one exit point in a method (this also makes easier to follow what is happening).
I'm working on an assignment for my java class, and we just started learning about HashMaps and we have this assignment where we create enumerated data and store it in a hashmap to print out later. What I can seem to figure out is to be able to print the elements of the HashMap. Here is my project so far:
public class Driver <enumeration>
{
private static HashMap<String, State> stateList = new HashMap<String, State>();
public static void main(String args[]) throws IOException
{
stateList.put("1", State.CA);
stateList.put("2", State.FL);
stateList.put("3", State.ME);
stateList.put("4", State.OK);
stateList.put("5", State.TX);
for(State value : stateList.values())
{
System.out.println(value);
}
}
}
public enum State
{
CA(new StateInfo("Sacramento", 38802500)), FL(new StateInfo("Tallahassee", 19893297)),
ME(new StateInfo("Augusta", 1330089)), OK(new StateInfo("Oklahoma City", 3878051)),
TX(new StateInfo(" Austin", 26956958));
private StateInfo info;
private State(StateInfo info)
{
this.info = info;
}
public StateInfo getInfo()
{
return info;
}
public String toString()
{
return "";
}
}
public class StateInfo
{
private String capital;
private int population;
public StateInfo(String capital, int population)
{
this.capital = capital;
this.population = population;
}
public String getCapital()
{
return capital.toString();
}
public int getPopulation()
{
return population;
}
public String toString()
{
return "";
}
}
Now when I try to run the program, it just terminates without even as much as a reference number for the state objects I'm trying to print. What I think is wrong is in the StateInfo class so I tried changing some things but to no prevail. Can anyone tell me if my suspensions are correct, or am I overlooking something?
You have overridden the toString() method in the State class:
public String toString()
{
return "";
}
Therefore you get no output at all as for every value the toString() method is called in your loop:
for(State value : stateList.values())
{
System.out.println(value);
}
To be more precise: You should get 5 empty lines.
Remove the toString()method in order to use Java's default toString() implementation which returns the classname+hashCode() or make it return e.g. "Capital: " + info.getCapital().
In a Gate class I have method public List<Signal> inspect(List<Signal> inputs) which should contain a combination of feed(), propagate(), and read(). That's the only method I have left to finish but getting an error. Could smb please help me with this method? NOTE: propagate() is left abstract to be overriden by childclasses of Gate class. The method public List<Signal> inspect(List<Signal> inputs) should combine feed(), propagate(), and read().
import java.util.*;
public abstract class Gate implements Logic {
private List<Wire> inputs;
private Wire output;
private String name;
public Gate(String name, List<Wire> ins, Wire out)
{
this.name = name;
this.output = out;
if(ins.size() == 0 || ins.isEmpty())
throw new ExceptionLogicParameters(false, 1, 0);
else
this.inputs = ins;
}
#Override
public void feed(List<Signal> inSigs)
{
if(inSigs.size() != inputs.size())
throw new ExceptionLogicParameters(false, inputs.size(), inSigs.size());
else
{
for(int i = 0; i < inSigs.size(); i++)
{
inputs.get(i).setSignal(inSigs.get(i));
}
}
}
#Override
public void feed(String name)
{
if(!(this.name.equals(name)))
throw new ExceptionLogicMalformedSignal(name.charAt(0), "Invalid logic input");
else
{
Signal signalValue = Signal.fromString(name.charAt(0));
}
}
#Override
public List<Signal> read()
{
List<Signal> signals = new ArrayList<>();
signals.add(output.getSignal());
return signals;
}
#Override
public abstract boolean propagate();
#Override
public List<Signal> inspect(List<Signal> inputs)
{
List<Signal> allMethods = new ArrayList<>();
allMethods.add(this.feed(inputs));
allMethods.add(this.propagate());
allMethods.add(this.read());
}
#Override
public String toString()
{
return this.name+"( " + inputs.toString() + " | " + output.toString() + " )";
}
#Override
public boolean equals(Object other)
{
if(other instanceof Gate)
{
Gate someGate = (Gate)other;
return (this.inputs == someGate.inputs) && (this.output.equals(someGate.output)
&& (this.name.equals(someGate.name)));
}
else
return false;
}
}
All your methods have no return type.
When you do this
allMethods.add(this.feed(inputs));
allMethods.add(this.propagate());
allMethods.add(this.read());
It would not return anything and hence nothing is added to the list which will throw error.
Your list of of type signal
List<Signal> allMethods = new ArrayList<>();
You need to change the return type of all methods to Signal to add them to the list. Like you cant add an Integer to a List<String> you cannot add anything else than type Signal to the List<Signal>
I'm no sure of your code logic and if you can change the return type or not, but changing all methods return type to Signal should work fine.
Also, you need a return statement for
public List<Signal> inspect(List<Signal> inputs)
You have to always return something if method is not void and the return type should be same as function type
I have
String selectedName = "ABC";
List<object> pgetName;
where object has variables such as id, name, version
I want to do the equivalent of
int first = pgetName.indexOf(selectedName);
int last = pgetName.lastIndexOf(selectedName);
as used for simple String Arrays. I've tried
int first = pgetName.getProperty("name").indexOf(processToStart);
and
int first = pgetName[].getName().indexOf(processToStart);
for example but they don't work. How do I do what I want to do? This is advanced Java for me being a noob...
Thanks in advance,
Here's an other approach (might be a little overkill but it shows you an other way). The idea is to override the indexOf and lastIndexOf method so it would verify against your field "name":
private static class TestObject {
String id, name, version;
public TestObject(String id, String name, String version) {
super();
this.id = id;
this.name = name;
this.version = version;
}
public String getId() {
return id;
}
public String getName() {
return name;
}
public String getVersion() {
return version;
}
}
public static void main(String[] args) {
List<TestObject> pgetName = new ArrayList<TestObject>() {
#Override
public int indexOf(Object o) {
if (o == null || this.isEmpty()) {
return -1;
}
int counter=0;
for (TestObject current : this) {
if (o.equals(current.getName())) {
return counter;
}
counter++;
}
return -1;
}
#Override
public int lastIndexOf(Object o) {
if (o == null || this.isEmpty()) {
return -1;
}
for (int i=this.size()-1; i>=0;i--) {
TestObject current = get(i);
if (o.equals(current.getName())) {
return i;
}
}
return -1;
}
};
pgetName.add(new TestObject("1", "name1", "ver1"));
pgetName.add(new TestObject("2", "name2", "ver2"));
pgetName.add(new TestObject("3", "name3", "ver3"));
pgetName.add(new TestObject("4", "name1", "ver4"));
int first = pgetName.indexOf("name1");
int last = pgetName.lastIndexOf("name1");
System.out.println("First: " + first + " - Last: " + last);
}
Result is:
First: 0 - Last: 3
For any Java object you can override the methods equals and hashCode (this is not really used but it is generally a good practice to implement both methods) in order to use the indexOf and lastIndexOf functions of java.util.List.
The contextual menu of eclipse generates a default implementation of both methods, letting you choose on which field the comparison should be done. Give it a try.
After the implementation of the methods above, you can use indexOf on List.
If I understand your question, you want to "find the index of an Object where one of the properties of the object is a specific value".
This isn't directly possible in Java (or most languages FWIW). You can achieve it pretty simply with a for loop, however:
public MyObject findObjectByName(MyObject[] objects, String name) {
for (MyObject object: objects) {
if (object.name.equal(name) {
return object;
}
}
return null;
}
If you want to find the index, you can do something similar:
public int findObjectIndex(MyObject[] objects, String name) {
for (int i = 0; i < objects.length; ++i)
if (objects[i].name.equal(name) {
return i;
}
}
return -1;
}
Now, this is the most naive approach you can take, and is often, but not always, the best approach. If you have a large number of objects, and you need to look up a lot by name, then you could be better off building an index once, and then look them up by the index:
public class MyObjectIndex {
final Map<String, MyObject> byName = new HashMap<String, MyObject>();
public MyObjectIndex(MyObject[] objects) {
for (MyObject object: objects) {
byName.put(object.getName(), object);
}
}
public getMyObjectWithName(String name) {
return byName.get(name);
}
}
suppose, I have a student class with roll number and name. I want to sort it out wrt roll number. I tried the following .Here is my code:
package CollectionDemo;
import java.util.*;
class student1 implements Comparable<student1>{
int rollNo;
String name;
student1(int rollNo,String name){
this.rollNo=rollNo;
this.name=name;
}
#Override
public boolean equals(Object o){
if((o instanceof student1) && (((student1)o).rollNo == rollNo)){
return true;
}
else
{
return false;
}
}
#Override
public int hashCode(){
return 1;
}
public int compareTo(student1 s) {
return s.rollNo;
}
public String toString(){
return "["+rollNo+","+name+"]";
}
}
public class treeSetDemo {
public static void main(String... a){
Set<student1> set=new TreeSet<student1>();
set.add(new student1(102,"Anu"));
set.add(new student1(101,"Tanu"));
set.add(new student1(103,"Minu"));
System.out.println("elements:"+set);
}
}
o/p: elements:[[102,Anu], [101,Tanu], [103,Minu]]
so, its not sorting:( how to make it correct .
thanks for your help.
================================================
thanks for all your help. The following code runs fine, but now I want to know how it works, if i comment out equals and hashcode method.
package CollectionDemo;
import java.util.*;
class student1 implements Comparable<student1>{
int rollNo;
String name;
student1(int rollNo,String name){
this.rollNo=rollNo;
this.name=name;
}
/* #Override
public boolean equals(Object o){
if((o instanceof student1) && (((student1)o).rollNo == rollNo)){
return true;
}
else
{
return false;
}
}
#Override
public int hashCode(){
return 1;
}
*/
public int compareTo(student1 s) {
System.out.println("hello:"+(this.rollNo-s.rollNo));
return this.rollNo-s.rollNo;
}
public String toString(){
return "["+rollNo+","+name+"]";
}
}
public class treeSetDemo {
public static void main(String... a){
Set<student1> set=new TreeSet<student1>();
set.add(new student1(102,"Anu"));
set.add(new student1(101,"Tanu"));
set.add(new student1(103,"Minu"));
System.out.println("elements:"+set);
}
}
OP:
run:
hello:-1
hello:1
elements:[[101,Tanu], [102,Anu], [103,Minu]]
BUILD SUCCESSFUL (total time: 0 seconds)
you have to change compareTo method in bellow way
public int compareTo(student1 s) {
if(s.rollNo == this.rollNo){
return 0;
}else if(s.rollNo > this.rollNo){
return -1;
}else{
return 1;
}
}
- If you want to sort on the basis of only one attribute, then go with java.lang.Comparable<T> Intereface, along with Collections.sort(List l).
- But if you aim is to sort it on the basis of more then one attribute then go for java.util.Comparator<T> along with Collections.sort(List l, Comparator c).
Eg:
import java.util.Comparator;
public class Fruit implements Comparable<Fruit>{
private String fruitName;
private String fruitDesc;
private int quantity;
public Fruit(String fruitName, String fruitDesc, int quantity) {
super();
this.fruitName = fruitName;
this.fruitDesc = fruitDesc;
this.quantity = quantity;
}
public String getFruitName() {
return fruitName;
}
public void setFruitName(String fruitName) {
this.fruitName = fruitName;
}
public String getFruitDesc() {
return fruitDesc;
}
public void setFruitDesc(String fruitDesc) {
this.fruitDesc = fruitDesc;
}
public int getQuantity() {
return quantity;
}
public void setQuantity(int quantity) {
this.quantity = quantity;
}
public int compareTo(Fruit compareFruit) {
int compareQuantity = ((Fruit) compareFruit).getQuantity();
//ascending order
return this.quantity - compareQuantity;
//descending order
//return compareQuantity - this.quantity;
}
public static Comparator<Fruit> FruitNameComparator
= new Comparator<Fruit>() {
public int compare(Fruit fruit1, Fruit fruit2) {
String fruitName1 = fruit1.getFruitName().toUpperCase();
String fruitName2 = fruit2.getFruitName().toUpperCase();
//ascending order
return fruitName1.compareTo(fruitName2);
//descending order
//return fruitName2.compareTo(fruitName1);
}
};
}
I think this implementation is close to recommended:
#Override
public int compareTo(Object other) {
if(other == null || !(other instanceOf student)){
throw new IllegalArgumentException();
}
student s = (student) other;
if(this.rollNo > s.rollNo){
return 1;
} else if (this.rollNo < s.rollNo){
return -1;
} else {
return 0;
}
}
If you are using Comparable interface then your compareTo() method should return the comparison not equals method , Google comparable example.
Check this link
In your compareTo method, you are just returning the value of the object you are comparing to. You need to return the difference, of the attribute of the invoking instance and passed instance.
So, change your compareTo method to the below one: -
#Override
public int compareTo(student1 s) {
return this.rollNo - s.rollNo;
}
NOTE: - Only sign is important for Collections.sort, so you don't really need an if-else block to return -1, 0, or 1. Just return the difference. That's all.
P.S : -
Your hashcode implementation is a very poor one. It will put every instances in the same bucket.
#Override
public int hashCode(){
return 1; // All the instances will have the same hashcode.
}
Ideally, you should use only those attributes to calculate the hashCode which you have used to compare your two instances, here its rollNo.
So, rather than returning simply a value 1, you can have some equations, that calculates your hashcode, taking into to consideration your rollNo and a large prime number also.
You can go through Effective Java - Item#9 for more explanation of this topic.
Now, that your code is working fine, lets move to your 2nd doubt.
equals and hashCode methods are not used when you want to compare two objects that will be used while sorting. We override equals and hashCode methods in order to check whether an instance is equal to another instance later on.
So, compareTo method is not concerned with whether you have ocerrided equals ad hashCode method or not. And you can also infer from name as to what the two methods does, and can they be related or not.
Moreover, equals method is defined in Object class, whereas compareTo method is declared in Comparable interface. So, they are not interrelated.
Check the documentation of these methods: - Object#equals, Object#hashCode, and Comparable#compareTo