TreeSet自定义比较器算法..字符串比较。

Question

给定输入字符串：

{ "200,400,7,1", "100,0,1,1", "200,200,3,1", "0,400,11,1", "407,308,5,1","100,600,9,1" } ,

我将其添加到TreeSet中，并希望按照第三个元素的顺序进行排序，因此期望的输出将是：

(100,0,1,1) (200,200,3,1) (407,308,5,1) (200,400,7,1) (100,600,9,1) (0,400,11,1)

但实际输出是：

(100,0,1,1)(0,400,11,1)(200,200,3,1)(407,308,5,1)(200,400,7,1)(100,600,9,1)

但由于11的字符串比较小于9，但在整数方面，11>9。我的期望输出有所不同。请建议一些解决方法。

import java.util.Comparator;
import java.util.TreeSet;

public class TreeSetComparator {

    public static void main(String[] args) {
        Comparator<String> comparator = new Comparator<String>() {
            @Override
            public int compare(String a, String b) {
                String aStr = a;
                String bStr = b;
                String[] splitA = aStr.split(",");
                String[] splitB = bStr.split(",");

                return splitA[2].compareTo(splitB[2]);
            }
        };

        String[] arr = { "200,400,7,1", "100,0,1,1", "200,200,3,1",
                "0,400,11,1", "407,308,5,1", "100,600,9,1" };

        TreeSet<String> ts = new TreeSet<String>(comparator);
        for (String str : arr) {
            ts.add(str);
        }

        for (String element : ts)
            System.out.print(element + " ");

    }
}

- Abhishek Choudhary

Answer 1

你正在按字典顺序排序（"123"排在"20"前面），你需要将它们转换成整数，然后进行比较：

不要这样做：

return splitA[2].compareTo(splitB[2]);

但是：

return Integer.valueOf(splitA[2]).compareTo(Integer.valueOf(splitB[2]));

不过，更清晰的方法是创建一个自定义对象来保存这四个不同的值，然后创建一个 Comparator 来比较该对象的第三个值：

下面的内容：

public class Main {
    public static void main (String[] args) {

        Comparator<CustomObject> sortOn3rdValue = new Comparator<CustomObject>() {
            @Override
            public int compare(CustomObject o1, CustomObject o2) {
                return o1.v3 < o2.v3 ? -1 : o1.v3 > o2.v3 ? 1 : 0;
            }
        };

        Set<CustomObject> objects = new TreeSet<CustomObject>(sortOn3rdValue);

        String[] arr = { "200,400,7,1", "100,0,1,1", "200,200,3,1", "0,400,11,1", "407,308,5,1", "100,600,9,1" };

        for(String a : arr) {
            objects.add(new CustomObject(a.split(",")));
        }

        for(CustomObject co : objects) {
            System.out.println(co);
        }
    }
}

class CustomObject {

    final int v1, v2, v3, v4;

    CustomObject(String[] strValues) {
        // assume strValues.lenght == 4
        v1 = Integer.valueOf(strValues[0]);
        v2 = Integer.valueOf(strValues[1]);
        v3 = Integer.valueOf(strValues[2]);
        v4 = Integer.valueOf(strValues[3]);
    }

    @Override
    public String toString() {
        return String.format("(%d,%d,%d,%d)", v1, v2, v3, v4);
    }
}

将会打印:

(100,0,1,1)
(200,200,3,1)
(407,308,5,1)
(200,400,7,1)
(100,600,9,1)
(0,400,11,1)

- Bart Kiers