使用比较器排序字符串长度

Question

在尝试根据元素字符串长度对数组进行排序时,我遇到了编译错误.我有一套开始,

Set<String> arraycat = new HashSet<String>();
//add contents to arraycat
String[] array = arraycat.toArray(new String[0]);
//array looks like this now:
//array=[cat,cataaaa,cataa,cata,cataaa]

我理想的是要排序到

array=[cat,cata,cataa,cataaa,cataaaa]

所以我有一个类型的比较器

class comp implements Comparator {

    public int compare(String o1, String o2) {
        if (o1.length() > o2.length()) {
            return 1;
        } else if (o1.length() < o2.length()) {
            return -1;
        } else {
            return 0;
        }
    }
}

然后我打电话给上课

Collections.sort(array, new comp());

但是,它抛出了两个编译错误:

comp is not abstract and does not override abstract method   compare(java.lang.Object,java.lang.Object) in java.util.Comparator
class comp implements Comparator {
^
testa.java:59: cannot find symbol
symbol  : method sort(java.lang.String[],comp)
location: class java.util.Collections
Collections.sort(array, new comp());
^2 errors

我很感激任何解决问题的线索.

Answer 1

您需要指定一个类型参数,以Comparator使您的实现工作.

class comp implements Comparator<String> {
  public int compare(String o1, String o2) {
    if (o1.length() > o2.length()) {
      return 1;
    } else if (o1.length() < o2.length()) {
      return -1;
    } else {
      return 0;
    }
  }
}

在Java 1.7及更高版本中,您还可以将此方法的主体简化为:

class comp implements Comparator<String> {
  public int compare(String o1, String o2) {
    return Integer.compare(o1.length(), o2.length());
  }
}

另外,对对象进行Collections.sort排序List.由于您要对数组进行排序,因此您应该使用Arrays.sort:

Arrays.sort(array, new comp());

Answer 2

Arrays.sort()如果数据源是a,则需要使用方法array.

例如,

String []array={"first","second","third","six"};

Arrays.sort(array,new Comparator<String>()
{
  public int compare(String s1,String s2)
   {
    return s1.length() - s2.length();
    }
});

或者将数组转换为List以使用Collections.sort()方法,

Collections.sort(Arrays.asList(array),new Comparator<String>()
{
  public int compare(String s1,String s2)
   {
    return s1.length() - s2.length();
    }
});

Answer 3

一内衬

上升

Arrays.sort(words, Comparator.comparingInt(String::length));

降序

Arrays.sort(words, Comparator.comparingInt(String::length).reversed());

Answer 4

通过使用流和比较器实现了相同的效果，如下所示-

Arrays.stream(array)
      .sorted(Comparator.comparingInt(String::length))
      .forEach(a -> System.out.print(a + " "));