一文搞定Collections工具类，操作集合事半功倍

1 排序操作

public class SortTest {
    public static void main(String[] args) {
        ArrayList nums = new ArrayList();
        nums.add(5);
        nums.add(54);
        nums.add(15);
        nums.add(1);
        nums.add(35);
        // [5, 54, 15, 1, 35]
        System.out.println(nums);
        Collections.reverse(nums);
        // [35, 1, 15, 54, 5]
        System.out.println(nums);
        Collections.sort(nums);
        //[1, 5, 15, 35, 54]
        System.out.println(nums);
        //每次随机排序
        Collections.shuffle(nums);
        System.out.println(nums);
    }
}

2 查找、替换操作

public class SearchTest {
    public static void main(String[] args) {
        ArrayList nums = new ArrayList();
        nums.add(2);
        nums.add(-5);
        nums.add(3);
        nums.add(0);
        System.out.println(nums);
        System.out.println(Collections.max(nums));
        Collections.replaceAll(nums, 0, 1);
        System.out.println(nums);
        Collections.sort(nums);
        System.out.println(nums);
    }
}

3 同步控制

public class SynchronizedTest {
    public static void main(String[] args) {
        Collection c=Collections.synchronizedCollection(new ArrayList());
        List list=Collections.synchronizedList(new ArrayList());
    }
}

4 设置不可变集合

public class UnmodifiableTest {
    public static void main(String[] args) {
        // 创建空的、不可改变的对象
        List unmodifiableList = Collections.emptyList();
        Map scores = new HashMap();
        scores.put("语文", 99);
        scores.put("数学", 98);
        Map unmodifiableMap = Collections.unmodifiableMap(scores);
        // java.lang.UnsupportedOperationException
        // unmodifiableList.add("1");
        //unmodifiableMap.put("英语", 80);
    }
}