我检查字符串数组是否已排序的方法有什么问题

Question

我正在做一个 Java 类，但我无法弄清楚我错在哪里。

我有一个名为 ArrayMethods 的类和一个必须用来查看我的数组是否已排序的方法。这是我的代码：

public class ArrayMethods
{
    String[] list; //instance variable
    /**
     * Constructor for objects of class ArrayMethods
     */
    public ArrayMethods(String[] list)
    {
        // initialise instance variables
        this.list = list;
    }

    /**
     * Determines if the array is sorted (do not sort)
     * When Strings are sorted, they are in alphabetical order
     * Use the compareTo method to determine which string comes first
     * You can look at the String compareTo method in the Java API
     * @return true if the array  is sorted else false.
     */
    public boolean isSorted()
    {
        boolean sorted = true;

        // TODO: Write the code to loop through the array and determine that each
        // successive element is larger than the one before it
        for (int i = 0; i < list.length - 1; i++){
            if (list[i].compareTo(list[i + 1]) < 0){
                sorted = true;
            }
        }
        return sorted;
    }
}

然后我有一个这样的数组测试器：

public class ArrayMethodsTester {
    public static void main(String[] args) {
        //set up
        String[] animals = {"ape", "dog", "zebra"};
        ArrayMethods zoo = new ArrayMethods(animals); 

        //test isSorted
        System.out.println(zoo.isSorted());
        System.out.println("Expected: true");

        String[] animals2 = {"ape", "dog", "zebra", "cat"};
        zoo = new ArrayMethods(animals2);         
        System.out.println(zoo.isSorted());
        System.out.println("Expected: false");

        String[] animals3 = {"cat", "ape", "dog", "zebra"};
        zoo = new ArrayMethods(animals3); ;
        System.out.println(zoo.isSorted());
        System.out.println("Expected: false");
    }
}

对于第一个数组，我确实得到了正确的结果，因为它是正常的，问题是我对其他 2 个得到了正确的结果，很明显这是错误的。我没有得到什么？

Answer 1

可以通过在循环内直接返回false 使其更简单

   for (int i = 0; i < list.length - 1; i++) {
        if (list[i].compareTo(list[i + 1]) > 0) {
            return false;
        }
    }
    return true;

Answer 2

public class ArrayMethods
{
    String[] list; //instance variable
    /**
     * Constructor for objects of class ArrayMethods
     */
    public ArrayMethods(String[] list)
    {
        // initialise instance variables
        this.list = list;
    }

    /**
     * Determines if the array is sorted (do not sort)
     * When Strings are sorted, they are in alphabetical order
     * Use the compareTo method to determine which string comes first
     * You can look at the String compareTo method in the Java API
     * @return true if the array  is sorted else false.
     */
    public boolean isSorted()
    {
        boolean sorted = true;

        // TODO: Write the code to loop through the array and determine that each
        // successive element is larger than the one before it
       for (int i = 0; i < list.length - 1; i++){
            if (list[i].compareTo(list[i + 1]) > 0){
                sorted = false;
                break;

            }
        }
        return sorted;
    }
}`

Answer 3

如果您喜欢 Java 8 流的语法，也可以使用它们（尽管这对它们来说不是一个完美的用例，因为您需要流的两个元素进行操作）：

public static boolean isSorted(final String[] array) {
    return !IntStream.range(1, array.length)
        .mapToObj(i -> new Pair<String>(array[i - 1], array[i])).parallel()
            .anyMatch(t -> t.first.compareTo(t.second) > 0);
}

代码使用了一个小的帮助类Pair

public static final class Pair<T> {
    final T first;
    final T second;

    private Pair(final T first, final T second) {
        this.first = first;
        this.second = second;
    }
}

此解决方案还可以并行运行，这将使其在大型阵列上运行时更快。

感谢Collect successive pairs from a stream 使用流访问一对元素