Arrays用法整理

本文将整理 java.util.Arrays 工具类比较常用的方法： 

本文介绍的方法基于JDK 1.7 之上。 

1.  asList方法  

 @SafeVarargs
 public static <T> List<T> asList(T... a) {
     return new ArrayList<>(a);
 }

   使用该方法可以返回一个固定大小的List，如： 

 List<String> stringList = Arrays.asList("Welcome", "To", "Java",
         "World!");

 List<Integer> intList = Arrays.asList(1, 2, 3, 4);

   
2. binarySearch方法  

 

binarySearch方法支持在整个数组中查找，如： 

 int index = Arrays.binarySearch(new int[] { 1, 2, 3, 4, 5, 6, 7 }, 6);

以及在某个区间范围内查找， 如： 

 public static int binarySearch(int[] a, int fromIndex, int toIndex,
                                int key) {
     rangeCheck(a.length, fromIndex, toIndex);
     return binarySearch0(a, fromIndex, toIndex, key);
 }

 int index = Arrays.binarySearch(new int[] { 1, 2, 3, 4, 5, 6, 7 }, 1, 6, 6);

3. copyOf及copyOfRange方法  


 


如： 

 String[] names2 = { "Eric", "John", "Alan", "Liz" };


         //[Eric, John, Alan]
         String[] copy = Arrays.copyOf(names2, 3);

         //[Alan, Liz]
         String[] rangeCopy = Arrays.copyOfRange(names2, 2,
                 names2.length);

4. sort方法  

 String[] names = { "Liz", "John", "Eric", "Alan" };
 //只排序前两个
 //[John, Liz, Eric, Alan]
 Arrays.sort(names, 0, 2);
 //全部排序
 //[Alan, Eric, John, Liz]
 Arrays.sort(names);

另外，Arrays的sort方法也可以结合比较器，完成更加复杂的排序。 

 public static <T> void sort(T[] a, Comparator<? super T> c) {
     if (LegacyMergeSort.userRequested)
         legacyMergeSort(a, c);
     else
         TimSort.sort(a, c);
 }

5. toString方法  

Arrays的toString方法可以方便我们打印出数组内容。 

如： 

 String[] names = { "Liz", "John", "Eric", "Alan" };
 Arrays.sort(names);
 System.out.println(Arrays.toString(names));

控制台将打印出  [Alan, Eric, John, Liz]  

6. deepToString方法  

如果需要打印二维数组的内容： 

int[][] stuGrades = { { 80, 81, 82 }, { 84, 85, 86 }, { 87, 88, 89 } }; 

如果直接用

 System.out.println(Arrays.toString(stuGrades));

那么得到的结果类似于 
     [[I@35ce36, [I@757aef, [I@d9f9c3]} 

这个时候得用 deepToString 方法才能得到正确的结果[[80, 81, 82], [84, 85, 86], [87, 88, 89]] 

 System.out.println(Arrays.deepToString(stuGrades));

7. equals方法  

使用Arrays.equals来比较1维数组是否相等。 

 String[] names1 = { "Eric", "John", "Alan", "Liz" };

         String[] names2 = { "Eric", "John", "Alan", "Liz" };

         System.out.println(Arrays.equals(names1, names2));

8. deepEquals方法  

Arrays.deepEquals能够去判断更加复杂的数组是否相等。 

 int[][] stuGrades1 = { { 80, 81, 82 }, { 84, 85, 86 }, { 87, 88, 89 } };

         int[][] stuGrades2 = { { 80, 81, 82 }, { 84, 85, 86 }, { 87, 88, 89 } };

         System.out.println(Arrays.deepEquals(stuGrades1, stuGrades2));

9. fill方法  

 int[] array1 = new int[8];
         Arrays.fill(array1, 1);
         //[1, 1, 1, 1, 1, 1, 1, 1]
   System.out.println(Arrays.toString(array1));