检查集合是否包含与某个特定值匹配的所有值

Question

I want to know what the best way to know if all values of a collection match a particular value.

List<Integer> listOfStrings = new ArrayList<Integer>();

All I want to know is if all the entries in the "listOfStrings" match a particular value; for instance there is no integer that is not '1'.

I need the fastest solution to this. I have a solution with me but it is very rudimentary.

Answer 1

Loop through it:

public boolean checkAll(ArrayList<String> list) {
    for(int i = 0; i < listOfStrings.size(); i++) {
        String candidate = listOfStrings.get(i);
        if(candidate == null || !candidate.equals("1")) {
            return false;
        }
    }
    return true;
}

Answer 2

You could just iterate over your list with a simple for loop, and compare every value with your certain value (say 1). If one value from your list is not equal to the certain value, just set a boolean to false.

Answer 3

Just do this

public boolean isFilled(String value, ArrayList<String> list)
{
    for(int i = 0; i < list.size(); i++)
    {
        String toTest = list.get(i);
        if(toTest == null || !toTest.equals(value)) {
            return false;
        }
    }

    return true;
}

Answer 4

In Java 8 you can use the allMatch method of a stream to achieve this.

public boolean allOnes(Collection<Integer> values) {
    return values.parallelStream().allMatch(i -> i == 1);
}

Using a parallelStream will potentially yield better performance if there are multiple processors available.

Answer 5

 boolean x=true;
     ArrayList<Integer> listOfInts = new ArrayList<Integer>   (Arrays.asList(5,3,1,2,9,5,0,7));
    Integer target = 1;
    for (int i = 0; i < listOfInts.size(); i++)
    {
        if (listOfInts.get(i).equals(target)) // nothing
        {

        } else {
            x = false;
            break;// exits loop right after this
        }
    }
    System.out.println(x);

Answer 6

To my astonishment, all the solutions proposed so far are just plain wrong, or contain a subtle bug, or could be more efficient.

Here's a solution that works fast whatever the kind of list is, and even if the list contains null elements:

public boolean listIsFilledWith(List<Integer> integers, int i) {
    Integer value = i; // transform the int into an Integer only once
    for (Integer element : integers) { // iterate using an iterator, to avoid performance problems with linked lists
        if (!value.equals(element)) { // value is not null, but element can be. Don't compare objects with == or !=
            return false; // return early
        }
    }
    return true;
}

Answer 7

Use the .contains() method that tells you whether the value exists in the list : http://docs.oracle.com/javase/1.4.2/docs/api/java/util/List.html#contains%28java.lang.Object%29

myList.contains(1);

Note: it uses the .equals() method of the contained object (it might be useful in your future developments).

HIH M.