public class ArrayMethodsTest
{
public static void main(String[] args)
{
int[] tester = {0,1,2,3,4,5};
ArrayMethods test = new ArrayMethods(tester);
for(int element : test)
{
System.out.print(element + " ");
}
test.shiftRight();
for(int element : test) //error: for-each not applicable to expression type
{
System.out.print(element + " ");
}
}
}
I figure what the problem is. Thanks to jigar joshi. However I still need to use the ArrayMethods methods for the tester that I created. I know that they work but how can it be possible to provide a tester class for an object that isn't an array since the methods are for arrays.
public class ArrayMethods
{
public int[] values;
public ArrayMethods(int[] initialValues)
{
values = initialValues;
}
public void swapFirstAndLast()
{
int first = values[0];
values[0] = values[values.length-1];
values[values.length-1] = first;
}
public void shiftRight()
{
int first = 0;
int second = first;
for(int i =0; i < values.length; i++)
{
if(i < values.length-1)
{
first = values[i];
second = values[i+1];
values[i+ 1] = first;
}
if(i == values.length)
{
values[i] = values[0];
}
}
}
}
//0,1,2,3,4,5
//5,0,1,2,3,4
test is reference of ArrayMethods which is not an Iterable or an array type and so is the error
You've already encountered the issue in which you can't iterate over an ArrayMethods, since it's not iterable. What it seems like you want to do is iterate over its values instead, considering that values is a public field.
for(int element : test.values) {
System.out.print(element + " ");
}
Related
I have created a function "m7" in my class but this function is always returning value getting multiplied by 2.
If I am running this function in "psvm" it is printing the right value.
In my Alice class, the method m7() is returning 10 which is incorrect but if I am running this method in psvm then it is returning 5 which is correct.
package com.math.functions;
import java.util.*;
public class Alice {
Integer[] rank= new Integer[7];
Integer n=65;
int count=0;
public Alice() {
rank[0]=100;
rank[1]=100;
rank[2]=90;
rank[3]=80;
rank[4]=75;
rank[5]=60;
rank[6]=n;
//rank[6]=20;
//rank[7]=10;
//rank[8]=n;
Arrays.sort(rank, Collections.reverseOrder());
}
public void print() {
for (Integer a : rank) {
System.out.println(a);
}
}
public int m7() {
for (int i = 0; i < rank.length; i++) {
if (rank[i] == n) {
break;
}
count++;
}
return count;
}
public void res(){
int s = m7();
System.out.println("this is the value of s here :"+s);
Set<Integer> hash_Set = new HashSet<>();
for(int i=0;i<=s/2;i++){
System.out.println("hii");
hash_Set.add(rank[i]);
}
for(Integer o:hash_Set){
System.out.println(o);
System.out.println("rank:"+hash_Set.size());
}
}
public static void main(String[] args) {
Alice a=new Alice();
a.print();
System.out.println("this is: "+a.m7());
a.res();
}
}
You are reusing the value of count from the previous time you run it.
Don't declare count as a member variable, make it a local variable.
public int m7() {
int count = 0; // HERE
for (int i = 0; i < rank.length; i++) {
if (rank[i] == n) {
break;
}
count++;
}
return count;
}
How can I alter the below method to work with an ArrayList?
I was thinking something like this:
public static boolean sortArrayList(ArrayList<Integer> list) {
return false;
}
but i'm not sure how to complete it.
Here is the method that I am trying to convert from working with an Array to instead work with an ArrayList:
public static boolean sortArrayList(final int[] data) {
for(int i = 1; i < data.length; i++) {
if(data[i-1] > data[i]) {
return false;
}
}
return true;
}
public static boolean sortArrayList(final ArrayList <Integer> data) {
for (int i = 1; i < data.size(); i++) {
if (data.get(i - 1) > data.get(i)) {
return false;
}
}
return true;
}
I have a few problems with the accepted answer, as given by #Sanj: (A) it doesn't handle nulls within the list, (B) it is unnecessarily specialized to ArrayList<Integer> when it could easily be merely Iterable<Integer>, and (C) the method name is misleading.
NOTE: For (A), it's quite possible that getting an NPE is appropriate - the OP didn't say. For the demo code, I assume that nulls are ignorable. Other interpretations a also fair, e.g. null is always a "least" value (requiring different coding, LAAEFTR). Regardless, the behaviour should be JavaDoc'ed - which I didn't do in my demo #8>P
NOTE: For (B), keeping the specialized version might improve runtime performance, since the method "knows" that the backing data is in an array and the compiler might extract some runtime efficiency over the version using an Iterable but such claim seem dubious to me and, in any event, I would want to see benchmark results to support such. ALSO Even the version I demo could be further abstracted using a generic element type (vs limited to Integer). Such a method might have definition like:
public static <T extends Comparable<T>> boolean isAscendingOrder(final Iterable<T> sequence)
NOTE: For (C), I follow #Valentine's method naming advice (almost). I like the idea so much, I took it one step further to explicitly call out the directionality of the checked-for-sortedness.
Below is a demonstration class that shows good behaviour for a isAscendingOrder which address all those issues, followed by similar behaviour by #Sanj's solution (until the NPE). When I run it, I get console output:
true, true, true, true, false, true
------------------------------------
true, true, true, true, false,
Exception in thread "main" java.lang.NullPointerException
at SortCheck.sortArrayList(SortCheck.java:35)
at SortCheck.main(SortCheck.java:78)
.
import java.util.ArrayList;
public class SortCheck
{
public static boolean isAscendingOrder(final Iterable<Integer> sequence)
{
Integer prev = null;
for (final Integer scan : sequence)
{
if (prev == null)
{
prev = scan;
}
else
{
if (scan != null)
{
if (prev.compareTo(scan) > 0)
{
return false;
}
prev = scan;
}
}
}
return true;
}
public static boolean sortArrayList(final ArrayList<Integer> data)
{
for (int i = 1; i < data.size(); i++)
{
if (data.get(i - 1) > data.get(i))
{
return false;
}
}
return true;
}
private static ArrayList<Integer> createArrayList(final Integer... vals)
{
final ArrayList<Integer> rval = new ArrayList<>();
for(final Integer x : vals)
{
rval.add(x);
}
return rval;
}
public static void main(final String[] args)
{
final ArrayList<Integer> listEmpty = createArrayList();
final ArrayList<Integer> listSingleton = createArrayList(2);
final ArrayList<Integer> listAscending = createArrayList(2, 5, 8, 10 );
final ArrayList<Integer> listPlatuea = createArrayList(2, 5, 5, 10 );
final ArrayList<Integer> listMixedUp = createArrayList(2, 5, 3, 10 );
final ArrayList<Integer> listWithNull = createArrayList(2, 5, 8, null);
System.out.print(isAscendingOrder(listEmpty ) + ", ");
System.out.print(isAscendingOrder(listSingleton) + ", ");
System.out.print(isAscendingOrder(listAscending) + ", ");
System.out.print(isAscendingOrder(listPlatuea ) + ", ");
System.out.print(isAscendingOrder(listMixedUp ) + ", ");
System.out.print(isAscendingOrder(listWithNull ) + "\n");
System.out.println("------------------------------------");
System.out.print(sortArrayList(listEmpty ) + ", ");
System.out.print(sortArrayList(listSingleton) + ", ");
System.out.print(sortArrayList(listAscending) + ", ");
System.out.print(sortArrayList(listPlatuea ) + ", ");
System.out.print(sortArrayList(listMixedUp ) + ", ");
System.out.print(sortArrayList(listWithNull ) + "\n");
}
}
Try below function, it takes integer array and converts it into a ArrayList and then computes the result :
public static boolean sortArrayList(final int[] data) {
List<Integer> aList = new ArrayList<Integer>();
for (int index = 0; index < data.length; index++)
aList.add(data[index]);
for (int i = 1; i < aList.size(); i++) {
if (aList.get(i - 1) > aList.get(i)) {
return false;
}
}
return true;
}
I have written a program which takes the words the user have entered, with a button press, and puts them in an ArrayList. There is also another text field where the user can enter a letter or word, for which the user can search for in the ArrayList with another button press. I'm using a sequential search algorithm to accomplish this, but it does not work as I expect it to; If the searched word is found, the search function should return, and print out in a textArea that the word was found and where in the array it was found. This works, but only for the first search. If the word is not found, the function should print out that the word was not found. This works as I want it to.
The problem is that after I searched for one word, and it displays where in the ArrayList this can be found, nothing happens when I press the button after that, whether the entered letter/word is in the array or not. It's like the string that the text gets stored isn't changing. I don't understand why... Here below is the custom Class of the search function and then my Main class:
public class Search {
static private int i;
static String index;
static boolean found = false;
public static String sequencial (ArrayList<String> list, String user) {
for (int i = 0; i < list.size(); i++) {
if (list.get(i).equals(user)) {
index = "The word " + user + " exist on the place " + i + " in the Arraylist";
found = true;
}
}
if (!found) {
index = "The word " + user + " could not be found";
}
return index;
}
My Main class:
ArrayList<String> list = new ArrayList<String>();
ArrayList<String> s = new ArrayList<String>();
private void btnAddActionPerformed(java.awt.event.ActionEvent evt) {
// TODO add your handling code here:
txtaOutput.setText("");
String word = txtfAdd.getText();
list.add(word);
for (int i = 0; i < list.size(); i++) {
txtaOutput.append("" + list.get(i) + "\n");
}
}
private void btnSearchActionPerformed(java.awt.event.ActionEvent evt) {
// TODO add your handling code here:
String user = txtfSearch.getText();
txtaOutput.setText("");
String index = Search.sequencial(list, user);
txtaOutput.setText("" + index);
}
Any help is appreciated!
The problem is that you declared your found variable as static. When your first word is found, it is set to true, and nothing ever sets it back to false. Instead of making it a static variable, declare it as a local variable inside your sequencial (it's spelled sequential, by the way) function, just before the for-loop.
In fact, all the variables you've declared as static should be made local. Declaring static variables is never a good idea.
As said by other users:
There is the List#indexOf(Object) method. You should use that instead of reinventing the wheel (unless you need to, and in that case you might have a look at the ArrayList implementation). There are also other collections, like HashSet which are more apropiate for looking up, but i guess that is another history.
The scope and the names of the variables (i, index, found) is error-prone. Do other methods or even classes need to have access to those variables? If you need to keep those variables, you might want to choose a visibility (public,protected,private). "index" is a misleading choice of a name for a message.
This would be an slightly simplified/corrected version of your code:
// Ommit those unneeded static variables
public static String sequencial (ArrayList<String> list, String user) {
int indexFound = list.indexOf(user);
if (user >= 0) {
return "The word " + user + " exist on the place " + indexFound + " in the Arraylist";
} else {
return "The word " + user + " could not be found";
}
}
...
private void btnSearchActionPerformed(java.awt.event.ActionEvent evt) {
String user = txtfSearch.getText();
// txtaOutput.setText("");
String seqMessage = sequencial(list, user);
txtaOutput.setText(seqMessage);
}
We use the static properties when you would like to use the constants. You should not use the static properties here. The problem will happen when your found property is changed the first time, it will not be changed again. And from that time, it will always be true. Similar with index property. Here is the code you can fix this:
public class Search {
public static SearchResult sequencial (ArrayList<String> list, String user) {
SearchResult result = null;
for (int i = 0; i < list.size(); i++) {
if (list.get(i).equals(user)) {
String index = "The word " + user + " exist on the place " + i + " in the Arraylist";
boolean found = true;
result = new SearchResult(index, found);
break;
}
}
if (result == null) {
String index = "The word " + user + " could not be found";
result = new SearchResult(index);
}
return result;
}
//sample inner class
static class SearchResult {
private String index;
private boolean found;
public SearchResult(String index) {
this.index = index;
}
public SearchResult(String index, boolean found) {
this.index = index;
this.found = found;
}
public String getIndex() {
return index;
}
public void setIndex(String index) {
this.index = index;
}
public boolean isFound() {
return found;
}
public void setFound(boolean found) {
this.found = found;
}
}
}
public class SequencialSearcher {
public static int SequencialSearchInt(int[] inputArray, int key)
{
for(int i=0; i < inputArray.length ; i++)
{
if(inputArray[i] == key)
{
return i;
}
}
return -1;
}
public static int SequencialSearchString(String[] array, String key)
{
for(int i=0; i < array.length ; i++)
{
if(array[i] == key)
{
return i;
}
}
return -1;
}
public static int SequencialSearchFloat(double[] array, double key)
{
for(int i=0; i < array.length ; i++)
{
if(array[i] == key)
{
return i;
}
}
return -1;
}
public static void main (String args[])
{
//select the type of the elements of search
//1 if integers
//2 if float
//3 if string
int x = 3;
int[] array1 = {9, 0, 10, 8, 5, 4, 6, 2, 3};
double[] array2 = {9.0, 0.0, 10.0, 8.0, 5.0, 4.0, 6.0, 2.0, 3.0};
String[] array3 = {"aa","hey", "hello"};
if(x == 1){
//enter the integer you want to search for here below
int requiredValue = 5;
int result = SequencialSearchInt(array1, requiredValue);
if (result != -1)
{
System.out.println("Required Value: "+requiredValue+" found at index: "+result);
}
else
{
System.out.println("Value:"+requiredValue+" not found");
}
}
else if(x == 2)
{
//enter the double you want to search for here below
double requiredValue1 = 5.0;
int result = SequencialSearchFloat(array2, requiredValue1);
if (result != -1)
{
System.out.println("Required Value: "+requiredValue1+" found at index: "+result);
}
else
{
System.out.println("Value:"+requiredValue1+" not found");
}
}
else if(x == 3){
//enter the string you want to search for here below
String requiredValue2 = "hey";
int result = SequencialSearchString(array3, requiredValue2);
if (result != -1)
{
System.out.println("Required Value: "+requiredValue2+" found at index: "+result);
}
else
{
System.out.println("Value:"+requiredValue2+" not found");
}
}
else{
System.out.println("Error. Please select 1,2 and 3 only");
}
}
}
I was wondering how can I use the remAll method on the very bottom of my code.
Whenever I try to use out.println(list.remAll());, it gives me an error saying
"No suitable method found for remAll"?
How can I fix this?
I have also tried using out.println(remAll(list));
I'm a beginner when it comes to Java and I am just learning, so pardon me if this is much simpler than it looks. P.S. Sorry if the format is wrong or something. It's my first post here.
import java.util.*;
import static java.lang.System.*;
public class StringArrayListLoader
{
public static void main(String args[])
{
Scanner kb = new Scanner(in);
out.print("Size of list? ");
int s = kb.nextInt();
ArrayList<String>list = new ArrayList<String>();
out.println("Enter the Strings: ");
for(int x = 0; x < s; x++)
{
out.print("String " + x + " :: ");
list.add( kb.next());
}
out.println("\nThe ArrayList you entered is ...");
out.println(list);
out.println(beginWithx(list) + " of the Strings begin with an \'x\'");
out.println(firstLast(list) + " of the Strings begin and end witletter.");
out.println("First String = Last String? " + firstLast2(list));
out.println(*******); // what am i supposed to put here?
}
public static int beginWithx(ArrayList<String>ar)
{
int count = 0;
for(int i = 0; i<ar.size(); i++)
if("x".equals(ar.get(i).substring(0,1)))
count++;
return count;
}
public static int firstLast(ArrayList<String>ar)
{
int counting = 0;
for(int i = 0; i<ar.size(); i++)
if(ar.get(i).substring(0,1).equals(ar.get(i).substring(ar.get(i).length()-2, ar.get(i).length()-1)))
counting++;
return counting;
}
public static boolean firstLast2(ArrayList<String>ar)
{
int counting = 0;
if(ar.get(0).equals(ar.get(ar.size()-1)))
return true;
return false;
}
public static void remAll(ArrayList<String>list, String s)
{
int i=0;
while(i<list.size())
{
if(list.get(i).equals(s))
{
list.remove(i);
}
else
{
i++;
}
}
out.println(list);
}
}
Your remAll method takes two parameters, an ArrayList<String> and a String. You must pass two parameters to call the method properly, such as
remAll(list, someOtherStringHere); // remAll has its own "out.println" calls
The method signature is
public static void remAll(ArrayList<String>list, String s)
So, you need to call it like:
remAll(list, "some string");
By inspection of the code, it will then remove all instances of "some string" from the list.
This is the zoo manager coding:
public class ZooManager {
public void feedAnimals(Animals a, Food[] arrayFood) {
Food temp = null;
for (int i = 0; i < arrayFood.length; i++) {
if (arrayFood[i].getFoodName().equals(a.getTypeOfFood())) {
arrayFood[i].setAmount(arrayFood[i].getAmount() - 1);
System.out.print("Animal is fed.");
}
}
System.out.print(temp);
}
public void isFoodEmpty(Food[] arrayFood) {
for (int i = 0; i < arrayFood.length; i++) {
if (arrayFood[i] == null) {
System.out.print("True");
} else {
System.out.print("False");
}
}
}
}
This is the code for the main application:
import java.util.Scanner;
public class ZooApp {
public static void main(String[] args) {
Scanner in = new Scanner(System.in);
Animals[] a = new Animals[4];
for (int i = 0; i < 4; i++) {
System.out.print("Enter the animal name: ");
String an = in.nextLine();
System.out.print("What type of food do they eat: ");
String tof = in.nextLine();
a[i] = new Animals(an, tof);
}
Food[] b = new Food[3];
for (int i = 0; i < 3; i++) {
System.out.print("Enter the type of food: ");
String f = in.nextLine();
System.out.print("Enter the amount: ");
int am = in.nextInt();in.nextInt();
b[i] = new Food(f, am);
}
ZooManager z= new ZooManager();
System.out.print(z.feedAnimals(a[i], b));
System.out.print(z.isFoodEmpty(b[i]));
}
}
I have an error at the two final out prints on the main application. The first one is that "the void type is not allowed there." and "variable i can not be found." The second out put says that "isFoodEmpty cannot be given to the type: Food, required: Food[]." Thank you for any advice or help.
Your isFoodEmpty function is a void, so the first error is telling you that you can't print it because it doesn't return anything. Second, you are passing an individual instance of Food into a function that is looking for an array. That's the second error. Also note that variable i is only defined within the scope of the for loop, so you can't go using it outside of the loop.
Edit:
Currently your isFoodEmpty is a void. you have one of two options:
public void isFoodEmpty(Food[] arrayFood) {
for (int i = 0; i < arrayFood.length; i++) {
if (arrayFood[i] == null) {
System.out.print("True");
} else {
System.out.print("False");
}
}
}
}
[...]
isFoodEmpty(b); // it already prints within the function
or
public boolean isFoodEmpty(Food[] arrayFood) {
for (int i = 0; i < arrayFood.length; i++) {
if (arrayFood[i] == null) {
return true;
} else {
return false;
}
}
}
}
[...]
System.out.println(isFoodEmpty(b)); // print the boolean that it returns
Either way, you might want to check the logic on that function, since it will return empty if even one of the elements in the array is null. (You could have 20 food items, then one null value, and it would return true).