Develop Reference

How can I declare an array in one function and use that same array in another function?

Here is my code
class Employee{
private String Animal;
private int Quantity;
Employee(String Animal, int Quantity){
this.Animal=Animal;
this.Quantity=Quantity;
public String getAnimal{
return animal;
}
public void setAnimal{
this.Animal=Animal;
}
public String getQuantity{
return Quantity;
}
public void setQuantity{
this.Quantity=Quantity;
}
public static void Input(){
Scanner sc = new Scanner(System.in);
int n = 0;
Employee[] list = new Employee[20];
list[no] = new Employee(" ", 0);
String nameOfAnimal = sc.nextLine();
list[n].setAnimal(nameOfAnimal);
String numberOfAnimal = sc.nextLine();
list[n].setQuantity(numberOfAnimal);
++n;
}
public static void Output(){
...
for(int i=0; i<n; ++i){
System.out.println(" -" + list[i].getAnimal + " - " + list[i].getQuantity);
}
}
}
In the Output method, I dot 3 points because I don't know how to get the array declared in the Input method and print its content within the Output method. It always shows an error that the first element is null when I create the same array in the Output function. Concisely, how can I keep an array that both functions can be used?

Not recognizing the class

This is the code that is meant to call a class called Couple and yet
it doesn't recognize the class why is this?
public class AgencyInterFace {
public static void main(String[] args) {
Scanner console = new Scanner(System.in);
Couple c = new Couple();
int choice, position;
showSelection();
choice = console.nextInt();
while (choice != 9) {
switch (choice) {
case 1:
addCouple();
break;
case 2:
position = console.nextInt();
testCouple(position);
break;
case 3:
position = console.nextInt();
displayCouple(position);
break;
case 9:
break;
default:
System.out.println("Invalid Selection");
} //end switch
showSelection();
choice = console.nextInt();
}
}
public static void showSelection() {
System.out.println("Select and enter");
System.out.println("1 - add a new couple");
System.out.println("2 - test a couple");
System.out.println("3 - display couple");
System.out.println("9 - exit");
}
public static void addCouple() {
Scanner console = new Scanner(System.in);
String herName, hisName;
int herAge, hisAge, ageDiff;
System.out.print("her name: ");
herName = console.nextLine();
System.out.print("her age: ");
herAge = console.nextInt();
System.out.print("his name: ");
hisName = console.nextLine();
System.out.print("his age: ");
hisAge = console.nextInt();
ageDiff = herAge - hisAge;
c.addData(herName, herAge, ageDiff, hisName, hisAge, ageDiff);
}
public static void testCouple(int position) {
System.out.println(c.test(position));
}
public static void displayCouple(int position) {
System.out.println(c.display(position));
}
public static void averageAge(int position) {
System.out.println(c.avgAge());
}
public static void maxDifference(int position) {
System.out.println(c.maxDif(position));
}
public static void averageDifference(int position) {
System.out.println(c.avgDif(position));
}
}//end of class
This code is the class that is meant to be called and that is not
being recognized and is unable to be called.
public class Couple {
final private int MAX = 5;
private Person[] p1, p2;
private int total;
public Couple() {
p1 = new Person[MAX];
p2 = new Person[MAX];
total = 0;
}
private void setData1(Person p, String name, int age, int ageDiff) {
p.setName(name);
p.setAge(age);
}
public String test(int pos) {
if (pos != -1) {
if (p1[pos].getAge() < p2[pos].getAge()) return ("GOOD FOR
"+p2[pos].getName()+" !");
else return ("GOOD
FOR "+p1[pos].getName()+" !");
}
return "error";
}
public void addData(String name1, int age1, int ageDiff1, String
name2, int age2, int ageDiff2) {
p1[total] = new Person();
p2[total] = new Person();
setData1(p1[total], name1, age1, ageDiff1);
setData1(p2[total], name2, age2, ageDiff2);
total++;
}
public String display(int position) {
if (position != -1)
return ("p1: " + p1[position].getName() + "
"+p1[position].getAge()+" / n "+" p2:
"+p2[position].getName()+"
"+p2[position].getAge());
else
return ("error");
}
public String avgAge(int position) {
double avg = 0;
double sum = 0.0;
for (int i = 0; i < position; i++) {
sum += p1[total].getAge();
sum += p2[total].getAge();
}
avg = sum / position;
return ("The average age is: " + avg);
}
public void ageDifference(int position) {
double ageDif = 0.0;
double ageSum = 0.0;
for (int i = 0; i < position; i++) {
if (p1[total].getAge() < p2[total].getAge()) {
ageSum = p2[total].getAge() - p1[total].getAge();
} else {
ageSum = p1[total].getAge() - p2[total].getAge();
}
ageSum = ageDif;
}
}
}
Is this have something to do with the name of the 'Couple' file or how
I call the class. I am getting an 'Undeclared Variable' error.

You defined c inside your main() method. Therefore it is not visible in your other methods. Either pass c as a parameter to your other methods or make it a (static) property of the AgencyInterFace class instead of a local variable of main().

USING STATIC METHODS
If you want to call a method of the class, e.g. test(int position), without creating a variable c, you need to make this method static:
public static String test(int pos) {
if (pos!=-1) {
if (p1[pos].getAge()<p2[pos].getAge()) return("GOOD FOR "+p2[pos].getName()+"!");
else return("GOOD FOR"+p1[pos].getName()+"!");
}
return "error";
}
In this case, your arrays p1[] and p2[] would also need to be static --> they would only be created one time.
And example for making your arrays static:
private static Person[] p1 = new Person[MAX],
p2 = new Person[MAX];
Now you can call this method of the class using Couple.test(position) and it will return a String.
USING NON-STATIC METHODS
If you want to create multiple references of the class Couple, in that p1[] and p2[] should contain different values, you need to create a reference of the class Couple.
You can implement this by telling the program, what c is:
Couple c = new Couple();
Edit:
I see that you have created a couple, but not at the right place. If you create your couple inside of the main() method, you cannot use it anywhere except in this method. You should declare it in your class:
public class AgencyInterFace {
private static Couple c = new Couple(); //<-- here
// main-method
// other methods
}

Printing an Array as a String with 10 elements per line

// Line in Main Code
public class Assignment7 {
public static void main(String[] args) {
Scanner scan = new Scanner(System.in);
String input;
char userChoice;
int newVal, index;
IntegerList intList = null;
printMenu();
do {
System.out.print("Please enter a command or type? ");
input = scan.nextLine();
if (input.length() != 0)
userChoice = input.charAt(0);
else
userChoice = ' ';
switch (userChoice) {
case 'a':
System.out.print("How big should the list be? ");
intList = new IntegerList(scan.nextInt());
scan.nextLine();
System.out.print("What is range of the values for each random draw? ");
intList.randomize(scan.nextInt());
scan.nextLine();
break;
case 'b':
System.out.println(intList.toStrng());
break;
The above code is part of my main code, where I get user input and as them to set the boundary conditions of the array. case 'b' asks to print out the array by calling the function in the class which should return the array as a string with 10 elements per line.
// line in class
import java.util.Arrays;
import java.util.Random;
public class IntegerList {
private int arrSize;
public IntegerList(int size) {
size = arrSize;
}
private int[] IntArray = new int[arrSize];
public void randomize (int num) {
for(int i = 0;i<IntArray.length;i++) {
IntArray[i] =(int) (Math.random()*(num+1));
}
}
public void addElement(int newVal, int index) {
for(int i = index;i<IntArray.length;i++) {
int temp = IntArray[i];
IntArray[i]=newVal;
IntArray[i+1]=temp;
if(i == IntArray.length){
increaseSize(IntArray);
}
}
}
private static void increaseSize(int[] x) {
int[] temp = new int[2*x.length];
for(int i = 0; i<x.length;i++) {
temp[i]=x[i];
}
x = temp;
}
public void removeFirst(int nextInt) {
// TODO Auto-generated method stub
}
public String range() {
// TODO Auto-generated method stub
return null;
}
public String toStrng() {
String arrayOut = " ";
for(int i = 0; i<IntArray.length; i++ ) {
if(i%10 == 0 ) {
arrayOut+="\n";
}
arrayOut += IntArray[i] + " " ;
}
return arrayOut;
}
}
I'm trying to convert the array into a string and then return int and have it display 10 elements per line. I'm pretty sure I have the logic right, however, when I run the code, it does not display the array at all. How should I go about fixing this?

Look at how you are creating your array of integers through your current constructor...
public IntegerList(int size) {
size = arrSize;
}
private int[] IntArray = new int[arrSize];
When you call
intList = new IntegerList(scan.nextInt());
in your menu program, your array list won't magically know it needs to be re-initialized. It will be 0 since the value of arrSize is always 0 when you create your IntegerList object. Furthermore you have the assignment of the variables switched. Change your constructor to the following
private int[] IntArray = null;
public IntegerList(int size) {
arrSize = size;
IntArray = new int[arrSize];
}
Everything seems to work because the size of your array was always 0 and your methods just return.

You did not initialize your arrSize
You can modify your constructor to initialize arrSize
public IntegerList(int size) {
arrSize = size;
}
Also, in you toStrng method, you can just make use of arrSize instead of IntArray.length

swapping of numbers using index in java is not working

package dspermutation;
import java.util.Scanner;
public class DSPermutation {
String s;
char[] c;
int n;
public static void main(String[] args) {
DSPermutation ds=new DSPermutation();
ds.input();
}
private void input() {
Scanner sc=new Scanner(System.in);
System.out.println("Enter the string");
s=sc.next();
c=s.toCharArray();
n=c.length;
permutation(c,n-1,0);
}
private void permutation(char[] cc,int nn,int ii) {
if(ii==nn)
{
System.out.println(cc);
}
else
{
for(int j=ii;j<=nn;j++)
{
swap(cc[ii],cc[j]);
permutation(cc,nn,ii+1);
swap(cc[ii],cc[j]);
}
}
}
private void swap(char p, char c0) {
int x=s.indexOf(p);
int y=s.indexOf(c0);
/*1*/ char temp=c[x];
/*2*/c[x]=c[y];
/*3*/c[y]=temp;
/*c[x]=c0;
c[y]=p;*/
}
}
The above program is for printing all permutations of a given string.The result is coming true but in swap() method if i replace line 1,2,3(written in comment) by logic written in comment(after line 1,2,3) then answer comes wrong. Why could this be happening?

Your mistake is assuming c[x] == p and c[y] == c0. But the indexes x and y are derived from the immutable string s, which doesn't reflect the values in c in its shuffled state.

You are swapping values of character array using immutable string's position (i.e String always holds the same initial values). To make your commented code work you have to add this s = String.valueOf(c);at the end of swap function.
private void swap(char p, char c0) {
int x = s.indexOf(p);
int y = s.indexOf(c0);
// char temp = c[x];
// c[x] = c[y];
// c[y] = temp;
c[y] = p;
c[x] = c0;
s = String.valueOf(c);
}

Values not printed out when using Comparator to sort ArrayList

I'm working on a program where I'm inputting values(String and int) into arrays, putting those values into an objects which go into an array list to be sorted by the the int value. When I run the program though, it prints out:
Sorted List Entries:
Item Name:null---Quant:0
Item Name:null---Quant:0
Item Name:null---Quant:0 //etc..
I'm trying to learn on my own here but I'm not sure what to do.
My main class:
import java.io.*;
import java.util.*;
public class InputItem
{
public static void main(String args[])
{
String again;
String names[] = new String[100];
int quant[] = new int[100];
int row=0;
do{
System.out.println("Please input assignment name:");
Scanner newName = new Scanner(System.in);
String name = newNamet.next();
names[row] =name;
System.out.println("Please input assignment quant:");
Scanner quantI = new Scanner(System.in);
int quantity = quantI.nextInt();
quant[row] = quantity;
System.out.println("Would you like to add another item? Enter 'Yes' or 'No'");
Scanner input = new Scanner(System.in);
again = input.next();
row++;
}
while(again.equalsIgnoreCase("Yes"));
List<Items> work = new ArrayList<Items>();
for(int count = 0; count<row; count++)
{
work.add(new Items((names[row]),(quant[row])));
}
Collections.sort(work, new MyComp());
System.out.println("Sorted List Entries: ");
for(Items e:work)
{
System.out.println(e);
}
}
}
Class with Comparator:
import java.util.*;
class MyComp implements Comparator<Items>
{
#Override
public int compare(Items e1, Items e2)
{
if((e1).getQuant()< (e2).getQuant())
{
return 1;
}
else
{
return -1;
}
}
}
public class Items
{
private String name;
private int quant;
public Items(String n, int q)
{
this.name = n;
this.quant = q;
}
public String getName()
{
return name;
}
public void setName(String name)
{
this.name = name;
}
public int getQuant()
{
return quant;
}
public void setQuant(int quant)
{
this.quant = quant;
}
public String toString()
{
return "Item Name:" + this.name+"---Quant:" +this.quant;
}
}

The problem is here...
for (int count = 0; count < row; count++) {
work.add(new Items((names[row]), (quant[row])));
}
You're using row, which was defined in the previous section of code to keep track of which element you were updating, but is now pointing to the next element in the array (or an empty element). This basically means you are constantly adding the same (empty) values to your Items
Instead, you should be using count
for (int count = 0; count < row; count++) {
work.add(new Items((names[count]), (quant[count])));
}