for (int i=1;i<10;i++)
{
if something == true
do something
else
do something
}
Here is what I want to do:
Outside the loop For, I need to summarize that at which i something = true and at which i something = false.
List<Integer> positiveResults = new ArrayList<Integer>();
List<Integer> negativeResults = new ArrayList<Integer>();
for (int i = 1; i < 10; i++)
{
if (someCondition)
positiveResults.add(i);
else
negativeResults.add(i);
}
where someCondition is supposed to be a boolean variable or expression.
If you explicitly want the results in an array instead of a List, then add
Integer[] resultsInArray = positiveResults.toArray(
new Integer[positiveResults.size()]);
You seem to have your for loop set up wrong, the conditional statement should be in the middle:
for (int i = 1; i < 10; i++)
but to answer the question, you just need to declare the variable before the loop:
int i = 1;
for ( ; i < 10; i++) {
}
// You can still access i here since it is still in scope.
First, your loop conditions are in the wrong order for what you probably want:
for (int i = 1; i < 10; ++i)
Next, I guess you want
if (something == true)
{
// do something
}
else
{
// do something *else*
}
in the loop body.
Anyway, in the do something part, you have the value of i since it's locally scoped. At that point you can add it to an array of your choosing.
Example with List:
List<Integer> trueStates = new ArrayList<Integer>();
for (int i=1;i<10;i++)
{
if (something == true) //e.g (i%2 == 0)
trueStates.add(i);
}
After for-loop you will have in trueState i which something == true. Another option is use Map which hold you state of all yours numbers.
Example with Map:
Map<Integer, Boolean> statesMap = new HashMap<Integer, Boolean>();
for (int i=1;i<10;i++)
{
statesMap.put(i, something == true);
}
Related
Why is this ArrayList empty when I print it out?
ArrayList<InterviewQuestion> interviewQuestionArrayList = new ArrayList<>();
for (int i = 0; i <interviewQuestionArrayList.size(); i++) {
interviewQuestionArrayList.add(new InterviewQuestion());
}
System.out.println(interviewQuestionArrayList);
You have created arraylist but before adding you are trying to looping through it.. size will be zero initially..
If you know how many interviewQuestions are there then you can loop with that number.
ex:
for (int i = 0; i <numberOfQuestions; i++) {
interviewQuestionArrayList.add(new InterviewQuestion());
}
numberOfQuestions should be predifined..
Initially if you dont know how many times you want to add then you can use while loop. But you should exit from while based on some condition
like,
boolean flag = true;
while(flag) {
interviewQuestionArrayList.add(new InterviewQuestion());
if(condition) flag = false;
} //something like this
As far as i can see, your List is empty when you enter the loop.
Thus its size() will return 0 and the loop will not add any elements.
your code basically does
for (int i = 0; i < 0; i++) {
interviewQuestionArrayList.add(new InterviewQuestion());
}
Here you create an empty list -> this means the size is currently 0
ArrayList<InterviewQuestion> interviewQuestionArrayList = new ArrayList<>();
The following loop is never executed because i (now 0) is never < size (now 0)
This means there are no Objects added to your list
for (int i = 0; i <interviewQuestionArrayList.size(); i++) {
interviewQuestionArrayList.add(new InterviewQuestion());
}
Try using i<10 as the condition in the for loop to add 10 elements to the list
if this 2 staments are followed by each other, then your list is never populated:
ArrayList<InterviewQuestion> interviewQuestionArrayList = new ArrayList<>();
for (int i = 0; i <interviewQuestionArrayList.size(); i++) {
interviewQuestionArrayList.add(new InterviewQuestion());
}
ergo, you have an empty list to print
System.out.println(interviewQuestionArrayList);
you can play with some dummyData that you add when declaring the list
I realize this has been asked before and I had a look at it but, for me, it only works to a point. After some struggle, I thought I'd ask.
I have an array of floats in an object's constructor.
That goes like this:
count = 3;
angles = new float[count];
The array length is really small though I'd like implement a modular and reusable approach.
I loop through the array assigning floats:
for (int i = 0; i < angles.length; i++) {
angles[i] = radians(random(360));
}
Then, with a new loop, I check if the singular elements have less than 30 degrees in between them, and if so, assign a new random value:
for (int i = 0; i < angles.length; i++) {
for (int k = i+1; k < angles.length; k++){
if(angles[i] != angles[k]){
if(abs(angles[i] - angles[k]) <= radians(30)){
angles[i] = radians(random(360));
}
}
}
}
This works nice and well but it doesn't guarantee that the new random number will keep the 30 degrees limit with the remaining elements. This, I assume, has to do with the length of the 'for' loop.
What would be the best way to overcome this and guarantee that newly fetched number will always conform to the 30 degree rule?
Instead of just checking once with an if statement, you could change it to a while statement, so that it attempts to find a new random number until the new one works.
while (abs(angles[i] - angles[k]) <= radians(30)){
angles[i] = radians(random(360));
}
However, if there are no numbers that follow your 30 degree rule, your program will get stuck in this loop, so you might want to check that there is a possible solution before entering the loop.
Edit: the above solution will ensure that the number follows the 30 degree rule with only one number in your array. Add a boolean to determine if the condition has been met, and loop until the boolean is true.
for (int i = 0; i < angles.length; i++) {
boolean meetsCondition = false;
while (!meetsCondition) {
for (int k = 0; k < angles.length; k++){
if(i != k){
if(abs(angles[i] - angles[k]) <= radians(30)){
angles[i] = radians(random(360));
meetsCondition = false;
break;
}
}
}
meetsCondition = true; //if the for loop completes, it has met the condition.
}
}
Why not use recursion earlier on:
for (int i = 0; i < angles.length; i++) {
angles[i] = findSuitable( i==0 ? 0 : angles[i-1] )
}
...
float findSuitable(float limit){
float sample = radians(random(360));
if(Math.abs(sample-limit) > 30)
return sample;
else
return findSuitable(limit);
}
In my opinion, you can try to change the the codes of random to this:
Random d = new Random();
int a = d.nextInt(360);
ArrayList<String> gradeN = new ArrayList<String>();
gradeN.add("one");
gradeN.add("two");
int num2 = 0;
while (num<5){
gradeN.get(0).concat("*");
num2++;
}
System.out.println(gradeN.get(0));
This is not working.
I want output like this:
one*****
and do this in a loop..
There are 2 mistakes in your code:
The variable incremented in your while loop is different to the one used in the condition.
Strings are immutable. String.concat returns a different String object and does not modify the original String. That means the value in your List is not modified. To fix this, use List.set to replace the old value in the list with a new one.
int num2 = 0;
while (num2 < 5) {
String newValue = gradeN.get(0).concat("*");
gradeN.set(0, newValue);
num2++;
}
Your question is somewhat unclear. Do you always want to add 5 stars to the string? If so, a constant string with 5 stars in it makes more sense than a loop. And I assume you really meant to do this for every element of gradeN? So something like this:
ArrayList<String> gradeN = new ArrayList<String>();
gradeN.add("one");
gradeN.add("two");
for (int i = 0; i < gradeN.size(); i++) {
gradeN.set(i, gradeN.get(i) + "*****");
System.out.println(gradeN.get(i));
}
If the number of stars added may vary and you really wanted to append them in a loop, then you could use StringBuilder to build it up:
ArrayList<String> gradeN = new ArrayList<String>();
gradeN.add("one");
gradeN.add("two");
int num = 5;
for (int i = 0; i < gradeN.size(); i++) {
StringBuilder stars = new StringBuilder(gradeN.get(i));
for (int j = 0; j < num; j++) {
stars.append('*');
}
gradeN.set(i, stars.toString());
System.out.println(gradeN.get(i));
}
One solution is to get the value of gradeN.get(0) on every loop and append * to it.
i.e.:
int num2 = 0;
while (num2<5){
gradeN.set(0, gradeN.get(0)+"*");
num2++;}
Output:
one*****
Demo:
http://ideone.com/XQvWqX
Please bear within as it might be difficult to understand
I have an array of jbuttons 50 size big, for this example ill use 7 I have jbutton object within 1 2 3 4 6 7 but not 5. These are printed on the screen. I want to remove these jbuttons however all buttons up to 5 are removed while the last two are not.
for(int i = 1; i < 51; i++){
if(seat.buttonArray[i] == null){
remove(seat.buttonArray[i]);
seat.buttonArray[i] = null;}
}
There is no way to remove element from array, assuming you want latter indexes changed after remove. For this purpose, you should use List:
Iterator buttonIterator = seat.buttonList.iterator();
while (buttonIterator.hasNext()) {
Object button = buttonIterator.next(); //or more specific type, if your list was generified
if (button == null) { //or some other criteria, wrote this just as an example
buttonIterator.remove();
}
}
If using array is mandatory, you have two options:
Set seat.buttonArray[i] to null value, indicating it has been removed;
Recreate array each time you deleted something. See System.arraycopy javadoc for details, although I do not recommend this approach because of performance considerations.
You could store the values in a temp array and then copy what you want back into your original array. Somewhat similar to this:
int myArray[50];
int temp[50];
int good;
for (int i = 0; i < 50; i++) {
myArray[i] = i;
}
for (int i = 0; i < 50; i++) {
temp[i] = myArray[i];
}
good = 0;
for (int i = 0; i < 50; i++) {
if (i < 10) {
} else {
myArray[good] = temp[i];
good += 1;
}
}
Looks messier than I first thought... But it essentially does what you're wanting.
I'm trying to write a small program that prints out distinct numbers in an array. For example if a user enters 1,1,3,5,7,4,3 the program will only print out 1,3,5,7,4.
I'm getting an error on the else if line in the function checkDuplicate.
Here's my code so far:
import javax.swing.JOptionPane;
public static void main(String[] args) {
int[] array = new int[10];
for (int i=0; i<array.length;i++) {
array[i] = Integer.parseInt(JOptionPane.showInputDialog("Please enter"
+ "an integer:"));
}
checkDuplicate (array);
}
public static int checkDuplicate(int array []) {
for (int i = 0; i < array.length; i++) {
boolean found = false;
for (int j = 0; j < i; j++)
if (array[i] == array[j]) {
found = true;
break;
}
if (!found)
System.out.println(array[i]);
}
return 1;
}
}
The simplest way would be to add all of the elements to a Set<Integer> and then just print the contents of the Set.
First of all, the "else if" statement is incorrect, since you don't provide any condition to the if (if you want an if, you need to write "if (condition) ...").
Second, you cannot decide inside the inner loop, if a value should be printed: The way your code works you write a value array[i] for each value array[j] that is different from array[i]!
Third: the inner loop needs only to go from 0 to the outer index i-1: For each element, you need only to decide, if it is the first occurrence (i.e. if the same value occured at any previous index or not). If it is, print it out, if not, ignore it.
A proper implementation of CheckDuplicate() would be:
public static void checkDuplicate(int array []) {
for (int i = 0; i < array.length; i++) {
boolean found = false;
for (int j = 0; j < i; j++)
if (array[i] == array[j]) {
found = true;
break;
}
if (!found)
System.out.println(array[i]);
}
}
But of course, some kind of Set would be much more efficient for bigger arrays...
EDIT: Of course, mmyers (see comments) is right by saying, that since CheckDuplicate() doesn't return any value, it should have return type void (instead of int). I corrected this in the above code...
Put them in a set ordered by insertion time, then convert back to an array if necessary.
new LinkedHashSet<Integer>(array).toArray()
Try throwing all of the integers into a Set. Duplicates will not ever be added to the Set and you will be left will a set of unique integers.
What you want can be accomplished using Java collection API, but not exactly as an one-liner, due to fact collection methods work with Objects and not primitives. J2SE lacks methods that convert, say, int[] to Integer[], but Apache Commons Lang library contains such useful methods, like ArrayUtils.toObject() and ArrayUtils.toPrimitive().
Using them, method to remove duplicated elements from an integer array looks something like this:
public static int[] removeDuplicates(int... array) {
Integer[] ints = ArrayUtils.toObject(array);
Set<Integer> set = new LinkedHashSet<Integer>(Arrays.asList(ints));
return ArrayUtils.toPrimitive(set.toArray(new Integer[set.size()]));
}
If your application is likely to include more of array/collection manipulation, I suggest you take a look at that library, instead of implementing things from scratch. But, if you're doing it for learning purposes, code away!
It would probably be better to add each number to a Set implementation rather than an array. Sets are specifically for storing collections of elements where you want to filter out duplicates.
Either use a Set as other people have suggested or use an List compatible class. With a list compatible class just use the Contains method to check if it already exists in the array.
import java.util.Scanner;
public class PrintDistinctNumbers {
/**
* #param args the command line arguments
*/
public static void main(String[] args) {
int [] numberArray = createArray();
System.out.println("The number u entered are: ");
displayArray(numberArray);
getDistinctNumbers(numberArray);
}
public static int[] createArray() {
Scanner input = new Scanner(System.in);
int [] numberCollection = new int [10];
System.out.println("Enter 10 numbers");
for(int i = 0; i < numberCollection.length; i++){
numberCollection[i] = input.nextInt();
}
return numberCollection;
}
public static void displayArray(int[] numberArray) {
for(int i = 0; i < numberArray.length; i++){
System.out.print(numberArray[i]+" ");
}
}
public static void getDistinctNumbers(int[] numberArray) {
boolean isDistinct = true;
int temp = 0;
int [] distinctArrayNumbers = new int [10];
for ( int i = 0; i < numberArray.length; i++){
isDistinct = true;
temp = numberArray[i];
for( int j = 0; j < distinctArrayNumbers.length; j++){
if( numberArray[i] == distinctArrayNumbers[j] ){
isDistinct = false;
}
}
if(isDistinct){
distinctArrayNumbers[temp]=numberArray[i];
temp++;
}
}
displayDistinctArray(distinctArrayNumbers);
}
public static void displayDistinctArray(int[] distinctArrayNumbers) {
for( int i = 0; i < distinctArrayNumbers.length; i++){
if(distinctArrayNumbers[i] != 0){
System.out.println(distinctArrayNumbers[i]);
}
}
}
}