We Keep Coding

How does the scope of this private method work?

My question is: how can I see the Tuple result in the process method if it was created in the check method? How am I able to use it there, if it was created in a private method?
public class Problem13 {
private Tuple<Integer> costs;
private Tuple<String> names;
private Tuple<Integer> result;
private int budget;
private int minDelta, minCost, totalCost;
public void process(String fileName) {
if (!read(fileName))
return;
if (budget >= totalCost) {
System.out.println("You can buy all items");
return;
}
if (budget < minCost) {
System.out.println("You cannot buy items");
return;
}
minDelta = -1;
int n = costs.getLength();
Set<Integer> interval = new IntegerInterval(0, n - 1);
for (int k = n - 1; k > 0; --k) {
Combinations<Integer> combinations = new Combinations<Integer>(interval, k);
combinations.produce((tuple) -> !check(tuple));
if (minDelta == 0)
break;
}
if (result == null)
System.out.println("No solution found");
else {
int k = result.getLength();
for (int j = 0; j < k; ++j)
System.out.printf("%s ", names.get(result.get(j)));
System.out.printf("(%d)\n", minDelta);
}
}
public static void main(String[] args) {
new Problem13().process("data/input13.txt");
}
private boolean check(Tuple<Integer> tuple) {
int k = tuple.getLength();
int currentCost = 0;
for (int i = 0; i < k; ++i) {
int j = tuple.get(i);
currentCost += costs.get(j);
if (currentCost > budget)
return false;
}
int d = budget - currentCost;
if (minDelta < 0 || d < minDelta) {
minDelta = d;
result = new ArrayTuple<>(k);
for (int i = 0; i < k; ++i)
result.set(i, tuple.get(i));
}
return minDelta == 0;
}

private means private to the class. So Problem13 can see anything defined in that class, whether private, public, protected or package private.
Also, the access modifier of the method only affects who can call it, not where the results can be seen. For instance, if result was defined as a public field, any class (not just Problem13) could see it.
You can find many good breakdowns of access modifiers out there on the Interwebs. Here's one.

Algorithm course: Output of int sort and method to sort Strings

My assignment asks me to make a TV show program, where I can input shows, delete, modify and sort them. What I'm stuck on is the sorting part. With the show, it asks for the name, day a new episode premieres, and time. Those are the keys I need to sort it by.
The program prompts the user to input one of those keys, then the program needs to sort (sorting by day will sort alphabetically).
I made a class and used an array. Here is the class:
public class showInfo
{
String name;
String day;
int time;
}
And the method to sort by time in the code:
public static void intSort()
{
int min;
for (int i = 0; i < arr.length; i++)
{
// Assume first element is min
min = i;
for (int j = i+1; j < arr.length; j++)
{
if (arr[j].time < arr[min].time)
{
min = j;
}
}
if (min != i)
{
int temp = arr[i].time;
arr[i].time = arr[min].time;
arr[min].time = temp;
}
}
System.out.println("TV Shows by Time");
for(int i = 0; i < arr.length; i++)
{
System.out.println(arr[i].name + " - " + arr[i].day + " - " + arr[i].time + " hours");
}
}
When I call it and output it in the main, it only shows "TV Shows by Time" and not the list. Why is this?
Also, I need to make ONE method that I will be able to use to sort both the day AND the name (both Strings). How can I do this without using those specific arrays (arr[i].name, arr[i].day) in the method?
Any help would be greatly appreciated! Thanks in advance!

In this part of your code
if (min != i) {
int temp = arr[i].time;
arr[i].time = arr[min].time;
arr[min].time = temp;
}
You're just changing the time when you should move the whole object instead. To fix it, the code must behave like this:
if (min != i) {
//saving the object reference from arr[i] in a temp variable
showInfo temp = arr[i];
//swapping the elements
arr[i] = arr[min];
arr[min] = temp;
}
I̶t̶ ̶w̶o̶u̶l̶d̶ ̶b̶e̶ ̶b̶e̶t̶t̶e̶r̶ ̶t̶o̶ ̶u̶s̶e̶ ̶ Arrays#sort ̶w̶h̶e̶r̶e̶ ̶y̶o̶u̶ ̶p̶r̶o̶v̶i̶d̶e̶ ̶a̶ ̶c̶u̶s̶t̶o̶m̶ ̶̶C̶o̶m̶p̶a̶r̶a̶t̶o̶r̶̶ ̶o̶f̶ ̶t̶h̶e̶ ̶c̶l̶a̶s̶s̶ ̶b̶e̶i̶n̶g̶ ̶s̶o̶r̶t̶e̶d̶ ̶(̶i̶f̶ ̶y̶o̶u̶ ̶a̶r̶e̶ ̶a̶l̶l̶o̶w̶e̶d̶ ̶t̶o̶ ̶u̶s̶e̶ ̶t̶h̶i̶s̶ ̶a̶p̶p̶r̶o̶a̶c̶h̶)̶.̶ ̶S̶h̶o̶r̶t̶ ̶e̶x̶a̶m̶p̶l̶e̶:̶
showInfo[] showInfoArray = ...
//your array declared and filled with data
//sorting the array
Arrays.sort(showInfoArray, new Comparator<showInfo>() {
#Override
public int compare(showInfo showInfo1, showInfo showInfo2) {
//write the comparison logic
//basic implementation
if (showInfo1.getTime() == showInfo2.getTime()) {
return showInfo1.getName().compareTo(showInfo2.getName());
}
return Integer.compare(showInfo1.getTime(), showInfo2.getTime());
}
});
//showInfoArray will be sorted...
Since you have to use a custom made sorting algorithm and support different ways to sort the data, then you just have to change the way you compare your data. This mean, in your current code, change this part
if (arr[j].time < arr[min].time) {
min = j;
}
To something more generic like
if (compare(arr[j], arr[min]) < 0) {
min = j;
}
Where you only need to change the implementation of the compare method by the one you need. Still, it will be too complex to create and maintain a method that can support different ways to compare the data. So the best option seems to be a Comparator<showInfo>, making your code look like this:
if (showInfoComparator.compare(arr[j], arr[min]) < 0) {
min = j;
}
where the showInfoComparator holds the logic to compare the elements. Now your intSort would become into something more generic:
public static void genericSort(Comparator<showInfo> showInfoComparator) {
//your current implementation with few modifications
//...
//using the comparator to find the minimum element
if (showInfoComparator.compare(arr[j], arr[min]) < 0) {
min = j;
}
//...
//swapping the elements directly in the array instead of swapping part of the data
if (min != i) {
int temp = arr[i].time;
arr[i].time = arr[min].time;
arr[min].time = temp;
}
//...
}
Now, you just have to write a set of Comparator<showInfo> implementations that supports your custom criteria. For example, here's one that compares showInfo instances using the time field:
public class ShowInfoTimeComparator implements Comparator<showInfo> {
#Override
public int compare(showInfo showInfo1, showInfo showInfo2) {
//write the comparison logic
return Integer.compare(showInfo1.getTime(), showInfo2.getTime());
}
}
Another comparator that uses the name field:
public class ShowInfoNameComparator implements Comparator<showInfo> {
#Override
public int compare(showInfo showInfo1, showInfo showInfo2) {
//write the comparison logic
return showInfo1.getName().compareTo(showInfo2.getName());
}
}
Now in your code you can call it like this1:
if (*compare by time*) {
genericSort(showInfoArray, new ShowInfoTimeComparator());
}
if (*compare by name*) {
genericSort(showInfoArray, new ShowInfoNameComparator());
}
if (*another custom rule*) {
genericSort(showInfoArray, new ShowInfoAnotherCustomRuleComparator());
}
where now you can implement a custom rule like compare showInfo objects using two or more fields. Taking as example your name and day fields (as stated in the question):
public class ShowInfoNameAndDayComparator implements Comparator<showInfo> {
#Override
public int compare(showInfo showInfo1, showInfo showInfo2) {
//write the comparison logic
int nameComparisonResult = showInfo1.getName().compareTo(showInfo2.getName());
if (nameComparisonResult == 0) {
return showInfo1.getDay().compareTo(showInfo2.getDay());
}
return nameComparisonResult;
}
}
1: There are other ways to solve this instead using lot of if statements, but looks like that's outside the question scope. If not, edit the question and add it to show another ways to solve this.
Other tips for your current code:
Declare the names of the classes using CamelCase, where the first letter of the class name is Upper Case, so your showInfo class must be renamed to ShowInfo.
To access to the fields of a class, use proper getters and setters instead of marking the fields as public or leaving the with default scope. This mean, your ShowInfo class should become into:
public class ShowInfo {
private String name;
private String day;
private int time;
public String getName() {
return this.name;
}
public void setName(String name) {
this.name = name;
}
//similar for other fields in the class
}

Use selection sort algorithm which is easy to implement,
for (int i = 0; i < arr.length; i++)
{
for (int j = i + 1; j < arr.length; j++)
{
if (arr[i].time > arr[j].time) // Here ur code that which should be compare
{
ShowInfo temp = arr[i];
arr[i] = arr[j];
arr[j] = temp;
}
}
}
no need to check min element. go through this wiki http://en.wikipedia.org/wiki/Selection_sort

Why not you use a Collection for this sort of a thingy to work. Moreover, in your added example, you are simply changing one attribute of a given object, while sorting, though you not changing the position of the object as a whole, inside the given list.
Create a List which will contain the references of all the Shows, now compare each attribute of one Show with another, in the List. Once the algorithm feels like, that swapping needs to be done, simply pick the reference from the List, save it in a temp variable, replace it with a new reference at this location, and set duplicate to the one stored in the temp variable. You are done, List is sorted :-)
Here is one small example for the same, for help :
import java.io.*;
import java.util.*;
public class Sorter {
private BufferedReader input;
private List<ShowInfo> showList;
public Sorter() {
showList = new ArrayList<ShowInfo>();
input = new BufferedReader(
new InputStreamReader((System.in)));
}
private void createList() throws IOException {
for (int i = 0; i < 5; i++) {
System.out.format("Enter Show Name :");
String name = input.readLine();
System.out.format("Enter Time of the Show : ");
int time = Integer.parseInt(input.readLine());
ShowInfo show = new ShowInfo(name, time);
showList.add(show);
}
}
private void performTask() {
try {
createList();
} catch (Exception e) {
e.printStackTrace();
}
sortByTime(showList);
}
private void sortByTime(List<ShowInfo> showList) {
int min;
for (int i = 0; i < showList.size(); i++) {
// Assume first element is min
min = i;
for (int j = i+1; j < showList.size(); j++) {
if (showList.get(j).getTime() <
showList.get(min).getTime()) {
min = j;
}
}
if (min != i) {
ShowInfo temp = showList.get(i);
showList.set(i, showList.get(min));
showList.set(min, temp);
}
}
System.out.println("TV Shows by Time");
for(int i = 0; i < showList.size(); i++) {
System.out.println(showList.get(i).getName() +
" - " + showList.get(i).getTime());
}
}
public static void main(String[] args) {
new Sorter().performTask();
}
}
class ShowInfo {
private String name;
int time;
public ShowInfo(String n, int t) {
name = n;
time = t;
}
public String getName() {
return name;
}
public int getTime() {
return time;
}
}
EDIT 2 :
For sorting By Name you can use this function :
private void sortByName(List<ShowInfo> showList) {
int min;
for (int i = 0; i < showList.size(); i++) {
// Assume first element is min
min = i;
for (int j = i+1; j < showList.size(); j++) {
int value = (showList.get(j).getName()).compareToIgnoreCase(
showList.get(min).getName());
if (value < 0)
min = j;
}
if (min != i) {
ShowInfo temp = showList.get(i);
showList.set(i, showList.get(min));
showList.set(min, temp);
}
}
System.out.println("TV Shows by Time");
for(int i = 0; i < showList.size(); i++) {
System.out.println(showList.get(i).getName() +
" - " + showList.get(i).getTime());
}
}
EDIT 3 :
Added Comparable<?> Interface, to the existing class to perform sorting based on specified input. Though one can improve on the logic, by using Enumeration, though leaving it for the OP to try his/her hands on :-)
import java.io.*;
import java.util.*;
public class Sorter {
private BufferedReader input;
private List<ShowInfo> showList;
private int command;
public Sorter() {
showList = new ArrayList<ShowInfo>();
input = new BufferedReader(
new InputStreamReader((System.in)));
command = -1;
}
private void createList() throws IOException {
for (int i = 0; i < 5; i++) {
System.out.format("Enter Show Name :");
String name = input.readLine();
System.out.format("Enter Time of the Show : ");
int time = Integer.parseInt(input.readLine());
ShowInfo show = new ShowInfo(name, time);
showList.add(show);
}
}
private void performTask() {
try {
createList();
} catch (Exception e) {
e.printStackTrace();
}
System.out.format("How would you like to sort : %n");
System.out.format("Press 0 : By Name%n");
System.out.format("Press 1 : By Time%n");
try {
command = Integer.parseInt(input.readLine());
} catch (Exception e) {
e.printStackTrace();
}
sortList(showList);
}
private void sortList(List<ShowInfo> showList) {
int min;
for (int i = 0; i < showList.size(); i++) {
// Assume first element is min
min = i;
for (int j = i+1; j < showList.size(); j++) {
showList.get(j).setValues(command);
int value = showList.get(j).compareTo(showList.get(min));
if (value < 0) {
min = j;
}
}
if (min != i) {
Collections.swap(showList, i, min);
}
}
System.out.println("TV Shows by Time");
for(int i = 0; i < showList.size(); i++) {
System.out.println(showList.get(i).getName() +
" - " + showList.get(i).getTime());
}
}
public static void main(String[] args) {
new Sorter().performTask();
}
}
class ShowInfo implements Comparable<ShowInfo> {
private String name;
private int time;
private int command;
public ShowInfo(String n, int t) {
name = n;
time = t;
}
public String getName() {
return name;
}
public int getTime() {
return time;
}
public void setValues(int cmd) {
command = cmd;
}
public int compareTo(ShowInfo show) {
int lastCmp = 1;
if (command == 0) {
lastCmp = name.compareTo(show.name);
} else if (command == 1) {
if (time < show.time) {
lastCmp = -1;
} else if (time == show.time) {
lastCmp = 0;
} else if (time > show.time) {
lastCmp = 1;
}
}
return lastCmp;
}
}

Using Arrays.sort, empty array returned

I'm using the Arrays.sort method to sort an array of my own Comparable objects. Before I use sort the array is full, but after I sort the array and print it to System nothing is printing out. EDIT. the array prints nothing at all. not empty line(s), just nothing.
here is the code for my method which uses sort :
public LinkedQueue<Print> arraySort(LinkedQueue<Print> queue1)
{
Print[] thing = new Print[queue1.size()];
LinkedQueue<Print> newQueue = new LinkedQueue<Print>();
for(int i = 0; i <queue1.size(); i++)
{
Print ob = queue1.dequeue();
thing[i] = ob;
System.out.println(thing[i]); //printing works here
}
Arrays.sort(thing);
for(int j = 0;j<thing.length-1;j++)
{
System.out.println(thing[j]); //printing does not work here
newQueue.enqueue(thing[j]);
}
return newQueue;
}
and here is the class for the Comparable object called Print.
public class Print implements Comparable<Print>
{
private String name;
private int numPages,arrivalTime,startTime,endTime;
public Print(String n, int p, int time, int sTime, int eTime)
{
name = n;
numPages = p;
arrivalTime = time;
startTime = sTime;
endTime = eTime;
}
public int getPages()
{
return numPages;
}
public int compareTo(Print other)
{
if(this.getPages()<other.getPages())
return -1;
else if(this.getPages()>other.getPages())
return 1;
else
return 0;
}
public String toString()
{
return name+"("+numPages+" pages) - printed "+startTime+"-"+endTime+" minutes";
}
}

Your last for loop doesn't print the last element in the array. If the array has only one element, it won't print anything at all. Change to:
for (int j = 0; j < thing.length; j++) //clean code uses spaces liberally :)
{
System.out.println(thing[j]);
newQueue.enqueue(thing[j]);
}
or (if supported by the JDK/JRE version used):
for (Print p : thing)
{
System.out.println(p);
newQueue.enqueue(p);
}

I hope the problem is this part of code
for(int i = 0; i <queue1.size(); i++)
{
Print ob = queue1.dequeue();
thing[i] = ob;
System.out.println(thing[i]); //printing works here
}
replace the above with
for(int i = 0; !queue1.isEmpty() ; i++)
{
Print ob = queue1.dequeue();
thing[i] = ob;
System.out.println(thing[i]); //printing works here
}

Method not working?

Updated code:
import java.util.*;
public class Main {
/**
* #param args
*/
static int[] C;
static int[] D;
static String P;
public static void main(String[] args) {
C = new int[10];
D = new int[10];
getNumber();
}
private static void getNumber() {
System.out
.println("Enter your first number with spaces in between digits.");
Scanner S = new Scanner(System.in);
String O = S.nextLine();
String[] A = new String[10];
A = O.split(" ");
for (int X = 0; A.length > X; X++) {
C[X] = toNumber(A[X]);
}
String P = S.nextLine();
String[] B = new String[10];
B = P.split(" ");
for (int Y = 0; B.length > Y; Y++) {
C[Y] = toNumber(A[Y]);
}
System.out.print(C[0]);
remainders();
}
private static void remainders() {
for (int A = 0; C.length > A; A++) {
if (D[1] * C[A] >= 10) {
Integer B = new Integer(D[1] * C[A]);
Character E = B.toString().charAt(0);
P.concat(E.toString());
}
}
for (int A = 0; C.length > A; A++) {
if (D[0] * C[A] >= 10) {
Integer B = new Integer(D[1] * C[A]);
Character E = B.toString().charAt(0);
P.concat(E.toString());
}
}
System.out.print(P);
}
private static int toNumber(String string) {
if (string.equals("0")) {
return 0;
} else if (string.equals("1")) {
return 1;
} else if (string.equals("2")) {
return 2;
} else if (string.equals("3")) {
return 3;
} else if (string.equals("4")) {
return 4;
} else if (string.equals("5")) {
return 5;
} else if (string.equals("6")) {
return 6;
} else if (string.equals("7")) {
return 7;
} else if (string.equals("8")) {
return 8;
} else if (string.equals("9")) {
return 9;
} else {
return 0;
}
}
}
For some reason, the last thing it prints is null. I am pretty sure the problem is the toNumber method, but I can't figure out what's wrong. If there are other problems with the code other than this, please let me know. Please help.
Edit: Problem seems to be with remainder method, please help

Use the string.equals(n) method to test if string is n

String constants are compared this way: "0".equals(string). String literals are actual String objects and You can call any String method on them. And you should prefer to call methods on constants, because it's guaranteed they exists, whereas variables can be null.
You don't need to reinvent the wheel. Java has rich SDK.
Simply use
int x = Integer.valueOf(a[X]);
If you want only numbers 0-9, then simply test
if (0 <= x && x <= 9) {
//valid continue
} else {
//invalid state handling
}

Recursive with void method?

I have a problem with one of my program (my programming language is java) :
I have an object Douglas-Peucker which is an array of Points and I have an algorithm, the Douglas-Peucker algorithm. I want to work directly on this array of Points and here the problem begin. This is Douglas-Peucker algorithm :
protected Point[] coinImage;
// My constructor
public Peucker(Point [] tab) {
coinImage = new Point[tab.length];
for(int i = 0; i < coinImage.length; i++) {
coinImage[i] = new Point(tab[i].x, tab[i].y);
}
}
public Point[] algoDouglasPeucker() {
return douglasPeuckerAux(0,coinImage.length - 1);
}
public Point[] douglasPeuckerAux(int startIndex, int endIndex) {
double dmax = 0;
int index = 0;
for(int i = startIndex + 1; i < endIndex; i++) {
double distance = this.distancePointSegment(this.coinImage[i], this.coinImage[startIndex], this.coinImage[endIndex]);
if(distance > dmax) {
index = i;
dmax = distance;
}
} ***
if(dmax >= this.epsilon) {
Point[] recResult1 = douglasPeuckerAux(startIndex,index);
Point[] recResult2 = douglasPeuckerAux(index,endIndex);
Point [] result = this.unionTabPoint(recResult1, recResult2);
return result;
}
else {
return new Point[] { coinImage[0],coinImage[endIndex] };
}
}
*** my problem is here : both methods have a specific type of return : array of Point or I want to change this because I want to work directly on my attribut (coinImage).
How change this in void methods ?
Help me please !
Sorry I forget one method : I also want to change the type of this method :
public Point[] unionTabPoint(Point [] P1,Point [] P2) {
Point[] res = new Point[P1.length + P2.length];
for(int i = 0; i < P1.length;i++) {
res[i] = new Point(P1[i].x,P1[i].y);
}
int k = 0;
for(int j = P1.length; j < res.length; j++) {
res[j] = new Point(P2[k].x,P2[k].y);
k++;
}
return res;
}
She return the union of two array but without specific order.

Well the basic layout for a void recursive method is like this:
int i = 0;
public void recursive(){
if(i == 6){
return;
}
i++;
recursive();
}
You can keep looping the method, as it would return the the next line, of the method that called it. In this case, the return, would reach the '}' and terminate the method, as it is finished.
Hope I helped :D

Java is doing call by reference. It is possible to use an local instance of your result and/or use it in your parameterlist, for example method(x, y, Point[]) and force the method as a result, what is your method call. Like:
public void doSome(x,y) { x==0 ? return : doSome(x-1, y-1); }

I hope this is what you looking for ...(if not pls clarify more)
public void douglasPeuckerAux(int startIndex, int endIndex) {
...
Point[] newCoinImage = new Point[] { coinImage[0],coinImage[endIndex] };
coinImage = newCoinImage;
}
public void unionTabPoint(Point [] P1,Point [] P2) {
...
coinImage = res;
}