Java中高效的判断数组中某个元素是否存在详解

public static boolean useList(String[] arr, String targetValue) {
  return Arrays.asList(arr).contains(targetValue);
}

public static boolean useSet(String[] arr, String targetValue) {
  Set<String> set = new HashSet<String>(Arrays.asList(arr));
  return set.contains(targetValue);
}

public static boolean useLoop(String[] arr, String targetValue) {
  for(String s: arr){
    if(s.equals(targetValue))
      return true;
  }
  return false;
}

public static boolean useArraysBinarySearch(String[] arr, String targetValue) { 
  int a = Arrays.binarySearch(arr, targetValue);
  if(a > 0)
    return true;
  else
    return false;
}

public static void main(String[] args) {
  String[] arr = new String[] { "CD", "BC", "EF", "DE", "AB"};

  //use list
  long startTime = System.nanoTime();
  for (int i = 0; i < 100000; i++) {
    useList(arr, "A");
  }
  long endTime = System.nanoTime();
  long duration = endTime - startTime;
  System.out.println("useList: " + duration / 1000000);

  //use set
  startTime = System.nanoTime();
  for (int i = 0; i < 100000; i++) {
    useSet(arr, "A");
  }
  endTime = System.nanoTime();
  duration = endTime - startTime;
  System.out.println("useSet: " + duration / 1000000);

  //use loop
  startTime = System.nanoTime();
  for (int i = 0; i < 100000; i++) {
    useLoop(arr, "A");
  }
  endTime = System.nanoTime();
  duration = endTime - startTime;
  System.out.println("useLoop: " + duration / 1000000);

  //use Arrays.binarySearch()
  startTime = System.nanoTime();
  for (int i = 0; i < 100000; i++) {
    useArraysBinarySearch(arr, "A");
  }
  endTime = System.nanoTime();
  duration = endTime - startTime;
  System.out.println("useArrayBinary: " + duration / 1000000);
}

useList: 13
useSet: 72
useLoop: 5
useArraysBinarySearch: 9

String[] arr = new String[1000];

Random s = new Random();
for(int i=0; i< 1000; i++){
  arr[i] = String.valueOf(s.nextInt());
}

useList: 112
useSet: 2055
useLoop: 99
useArrayBinary: 12

String[] arr = new String[10000];

Random s = new Random();
for(int i=0; i< 10000; i++){
  arr[i] = String.valueOf(s.nextInt());
}

useList: 1590
useSet: 23819
useLoop: 1526
useArrayBinary: 12

import org.apache.commons.lang3.ArrayUtils;
public static boolean useArrayUtils(String[] arr, String targetValue) {
  return ArrayUtils.contains(arr,targetValue);
}

useList: 323
useSet: 3028
useLoop: 141
useArrayBinary: 12
useArrayUtils: 181
-------
useList: 3703
useSet: 35183
useLoop: 3218
useArrayBinary: 14
useArrayUtils: 3125

  if(array == null) {
    return -1;
  } else {
    if(startIndex < 0) {
      startIndex = 0;
    }

    int i;
    if(objectToFind == null) {
      for(i = startIndex; i < array.length; ++i) {
        if(array[i] == null) {
          return i;
        }
      }
    } else if(array.getClass().getComponentType().isInstance(objectToFind)) {
      for(i = startIndex; i < array.length; ++i) {
        if(objectToFind.equals(array[i])) {
          return i;
        }
      }
    }

    return -1;
  }