Java list和数组的相互转换

    /**
     * 不推荐，添加时会报错
     */
    @Test
    public void arrry2List1() {
        //arrry to list
        String [] array = new String [10000];
        for (int i = 10000; i > 0; i--) {
            array[i] = String.valueOf(Math.round(10000));
        }
        List<String> list = Arrays.asList(array);
        list.add("d");//UnsupportedOperationException异常
        System.out.println(list);
    }

    /**
     * 第一种方式最快一般用第一种方式
     */
    @Test
    public void arrry2List2() {
        //arrry to list
        String [] array = new String [1000000];
        for (int i = 0; i < 1000000; i++) {
            array[i] = String.valueOf(Math.round(1000000));
        }
        //new ArrayList<>(Arrays.asList(array)
        long start = System.currentTimeMillis();
        List<String> list = new ArrayList<>(Arrays.asList(array));
        System.out.println("耗时：" + (System.currentTimeMillis() - start));

        //Collections.addAll(list2,array);
        start = System.currentTimeMillis();
        List<String> list2 = new ArrayList<>(array.length);
        Collections.addAll(list2,array);
        System.out.println("耗时：" + (System.currentTimeMillis() - start));

        //stream 1
        start = System.currentTimeMillis();
        List<String> list3 = Stream.of(array).collect(Collectors.toList());
        System.out.println("耗时：" + (System.currentTimeMillis() - start));

        //stream 2
        start = System.currentTimeMillis();
        List<String> list4 = Arrays.stream(array).collect(Collectors.toList());
        System.out.println("耗时：" + (System.currentTimeMillis() - start));

        //    耗时：4
        //    耗时：8
        //    耗时：51
        //    耗时：11
    }

    /**
     * 第一种方式最快一般用第一种方式
     */
    @Test
    public void list2Arrry() {
        //arrry to list
        List<String> list = new ArrayList<>(1000000);
        for (int i = 0; i < 1000000; i++) {
            list.add(String.valueOf(Math.round(1000000)));
        }
        //new ArrayList<>(Arrays.asList(array)
        long start = System.currentTimeMillis();
        String[] array = new String[list.size()];
        String[] strings = list.toArray(array);
        System.out.println("耗时：" + (System.currentTimeMillis() - start));


        //stream 1
        start = System.currentTimeMillis();
        String[] strings1 = list.stream().toArray(String[]::new);
        System.out.println("耗时：" + (System.currentTimeMillis() - start));

//        耗时：8
//        耗时：51
    }

尽量不使用stream，原始转换速度更快

本文地址：https://blog.csdn.net/cyy356/article/details/110235600