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(array1.toString())