4.1 元素排序/查找元素位置 Arrays.sort、Arrays.binarySearch

public static void main(String args[]) throws Exception {
    int array[] = { 2, 5, -2, 6, -3, 8, 0, -7, -9, 4 };
    Arrays.sort(array);
    printArray("数组排序结果为", array); // -9, -7, -3, -2, 0, 2, 4, 5, 6, 8
    int index = Arrays.binarySearch(array, 2);
    System.out.println("元素 2  在第 " + index + " 个位置");
}

4.2 获取最大值和最小值 Collections 工具类

Integer[] numbers = { 8, 2, 7, 1, 4, 9, 5};
int min = (int) Collections.min(Arrays.asList(numbers));
int max = (int) Collections.max(Arrays.asList(numbers));

4.3 数组合并 Arrays.asList、addAll

public class Main {
    public static void main(String args[]) {
        String a[] = { "A", "E", "I" };
        String b[] = { "O", "U" };
        List list = new ArrayList(Arrays.asList(a));
        list.addAll(Arrays.asList(b));
        Object[] c = list.toArray();
        System.out.println(Arrays.toString(c));
    }
}

4.4 数组填充 Arrays.fill

public class FillTest {
    public static void main(String args[]) {
        int array[] = new int[6];
        Arrays.fill(array, 100); // 100, 100, 100, 100, 100, 100
        for (int i=0, n=array.length; i < n; i++) {
            System.out.println(array[i]);
        }
        System.out.println();
        Arrays.fill(array, 3, 6, 50); // 100, 100, 100, 50, 50, 50
        for (int i=0, n=array.length; i< n; i++) {
            System.out.println(array[i]);
        }
    }
}

4.5 数组扩容/复制 System.arraycopy

String[] names = new String[] { "A", "B", "C" };
String[] extended = new String[5];
System.arraycopy(names, 0, extended, 0, names.length); // A, B, C, NULL, NULL

4.6 数组交集 retainAll

public class Main {
    public static void main(String[] args)  {
        ArrayList objArray = new ArrayList(); ArrayList objArray2 = new ArrayList();
        objArray2.add(0,"common1"); objArray2.add(1,"common2"); objArray2.add(2,"notcommon");
        objArray2.add(3,"notcommon1"); objArray.add(0,"common1"); objArray.add(1,"common2"); objArray.add(2,"notcommon2");
        System.out.println("array1 数组元素："+objArray); // [common1, common2, notcommon2]
        System.out.println("array2 数组元素："+objArray2); // [common1, common2, notcommon, notcommon1]
        objArray.retainAll(objArray2);
        System.out.println("array2 & array1 数组交集为："+objArray); // [common1, common2]
    }
}

4.7 数组差集 removeAll

public class Main {
    public static void main(String[] args)  {
        ArrayList objArray = new ArrayList(); ArrayList objArray2 = new ArrayList();
        objArray2.add(0,"common1"); objArray2.add(1,"common2"); objArray2.add(2,"notcommon");
        objArray2.add(3,"notcommon1"); objArray.add(0,"common1"); objArray.add(1,"common2"); objArray.add(2,"notcommon2");
        System.out.println("array1 数组元素："+objArray); // [common1, common2, notcommon2]
        System.out.println("array2 数组元素："+objArray2); // [common1, common2, notcommon, notcommon1]
        objArray.removeAll(objArray2);
        System.out.println("array1 与 array2 数组差集为："+objArray); // [notcommon2]
    }
}

4.8 查找元素是否存在 contains

ArrayList<String> objArray = new ArrayList<String>();
objArray.add(0,"common1"); objArray.add(1,"common2");
objArray.contains("common2"); // true

4.9 数组比较 Arrays.equals

int[] ary = {1,2,3,4,5,6}; int[] ary1 = {1,2,3,4,5,6};
Arrays.equals(ary, ary1); // true