如何检查数组是否为空或数组内容是否为空

Question

What is the best way to check if array is null value or if the array contents are null in combination in 1 statement in Java 6:

if ((myArray[0] != null) || (myArray[1] != null) || (myArray!= null)) {
    ...
}

Answer 1

Firstly, check if the array is not null itself. If the array is null , it makes no reason to iterate its elements since Java will throw the NullPointerException upon access to it:

if (myArray != null) {
    // ...
}

Then inside the body of the condition iterate through all its elements and check if one of them is null .

boolean hasNull = false;
for (int i=0; i<myArray.length; i++) {
    if (myArray[i] == null) {
        hasNull = true;
        break; // to terminate the iteration since there is no need to iterate more
    } 
}

---

This one-line solution (thanks for the warning from @Napstablook). The condition is evaluated as true if the array itself is null or one of its element is null :

if !(myArray != null && myArray[0] != null && myArray[1] != null) { ... }

Be aware that the && operator works that if the left side is evaluated as false , it stops evaluating the rest of the condition because it will not affect the result. The same does || but with true . However, I suggest you avoid this solution since the index might overflow. Better use the for-loop mentioned above.

Answer 2

To have it check for any value, I'd use allMatch . It's also important to check for array != null first, otherwise you'll get an Exception if it is.

if (array == null || Arrays.stream(array).allMatch(Objects::isNull)) 

Note that this won't work with java prior to version 8, OP edited his requirements after I posted the answer

Answer 3

Check if Array is null:

String array[] = null;
if (array == null) {
  System.out.println("array is null");
}

Check if array is Empty:

array = new int[0];
if (array.length == 0) {
  System.out.println("array is empty");
}

Check for null at the same time:

int[] array = ...;
if (array.length == 0) { } // no elements in the array

if (array == null || iarray.length == 0) { }

Answer 4

Try this

 if (myArray == null || Arrays.stream(myArray).allMatch(element-> element==null)) {}

Edit- For java 6, I really don't see this happening in one line. You can try this if one line is not necessary

  boolean isNull = true;
    if(myArray==null){
        System.out.println("array is null");
    }else{
        for(Integer element: myArray){
            if(element!=null){
                System.out.println("array is not null");
                isNull=false;
                break;
            }
        }
        if(isNull)
            System.out.println("Array is null");
    }

Answer 5

for example this

boolean isNullOrContainsNull = array == null || Arrays.asList(array).contains(null);

checks in a line whether the array is null or contains null elements

If you want to check whether the array is null or empty or all elements are null take

boolean containsNothingUseful = array == null
        || array.length == 0
        || !new HashSet<String>(Arrays.asList(array))
            .retainAll(Arrays.asList((String)null));

(assuming a String[] array)

Uses the Collection#retainAll() method which returns true when there were other values present, ie the inverse of "containsOnly"

Using this one liner is actually fairly inefficient and one better uses a method like below which doesn't create lots of temporary objects and mutates collections etc.

public static boolean containsNothingUseful(String[] array) {
    if (array == null || array.length == 0)
        return true;
    for (String element : array) {
        if (element != null)
            return false;
    }
    return true;
}

// ...
if (containsNothingUseful(myArray)) { .. }

Answer 6

Instead Itreating Manullay the array, re use the existing collection for this case.

1. Convert Array Into List
2. Check Null is present in list or not using contains() method;

Please find the sample code:

public static void main(String[] args) {
        Integer[] array = new Integer[3];

        array[0] = 1;
        array[1] = null;
        array[2] = 2;

        System.out.println(Arrays.asList(array).contains(null));
    }