迭代数组 - java

Question

I was wondering if it was better to have a method for this and pass the Array to that method or to write it out every time I want to check if a number is in the array .

For example:

public static boolean inArray(int[] array, int check) {

    for (int i = 0; i < array.length; i++) {
        if (array[i] == check) 
            return true;
    }

    return false;
}

Thanks for the help in advance!

Answer 1

Since atleast Java 1.5.0 (Java 5) the code can be cleaned up a bit. Array s and anything that implements Iterator (eg Collection s) can be looped as such:

public static boolean inArray(int[] array, int check) {
   for (int o : array){
      if (o == check) {
         return true;
      }
   }
   return false;
}

In Java 8 you can also do something like:

// import java.util.stream.IntStream;

public static boolean inArray(int[] array, int check) {
   return IntStream.of(array).anyMatch(val -> val == check);
}

Although converting to a stream for this is probably overkill.

Answer 2

You should definitely encapsulate this logic into a method.

There is no benefit to repeating identical code multiple times.

Also, if you place the logic in a method and it changes, you only need to modify your code in one place.

Whether or not you want to use a 3rd party library is an entirely different decision.

Answer 3

If you are using an array (and purely an array), the lookup of "contains" is O(N) , because worst case, you must iterate the entire array. Now if the array is sorted you can use a binary search, which reduces the search time to log(N) with the overhead of the sort.

If this is something that is invoked repeatedly, place it in a function:

private boolean inArray(int[] array, int value)
{  
     for (int i = 0; i < array.length; i++)
     {
        if (array[i] == value) 
        {
            return true;
        }
     }
    return false;  
}  

Answer 4

You can import the lib org.apache.commons.lang.ArrayUtils

There is a static method where you can pass in an int array and a value to check for.

contains(int[] array, int valueToFind) Checks if the value is in the given array.

ArrayUtils.contains(intArray, valueToFind);

ArrayUtils API

Answer 5

Using java 8 Stream API could simplify your job.

public static boolean inArray(int[] array, int check) {
    return Stream.of(array).anyMatch(i -> i == check);
}

It's just you have the overhead of creating a new Stream from Array , but this gives exposure to use other Stream API. In your case you may not want to create new method for one-line operation, unless you wish to use this as utility. Hope this helps!