我有对象数组person (int age;字符串名称;)。

我如何按名字的字母顺序排序这个数组,然后按年龄?

你会用哪种算法呢?


当前回答

当使用Guava的ComparisonChain时,我会很小心,因为它会为每个被比较的元素创建一个实例,所以如果你在排序,你会看到N x Log N个比较链的创建,或者如果你在迭代和检查相等,则会有N个实例。

如果可能的话,我会使用最新的Java 8 API或Guava的ordered API创建一个静态比较器,这里是Java 8的一个例子:

import java.util.Comparator;
import static java.util.Comparator.naturalOrder;
import static java.util.Comparator.nullsLast;

private static final Comparator<Person> COMPARATOR = Comparator
  .comparing(Person::getName, nullsLast(naturalOrder()))
  .thenComparingInt(Person::getAge);

@Override
public int compareTo(@NotNull Person other) {
  return COMPARATOR.compare(this, other);
}

以下是如何使用番石榴的订购API: https://github.com/google/guava/wiki/OrderingExplained

其他回答

您需要实现自己的Comparator,然后使用它:例如

Arrays.sort(persons, new PersonComparator());

你的比较器可以看起来像这样:

public class PersonComparator implements Comparator<? extends Person> {

  public int compare(Person p1, Person p2) {
     int nameCompare = p1.name.compareToIgnoreCase(p2.name);
     if (nameCompare != 0) {
        return nameCompare;
     } else {
       return Integer.valueOf(p1.age).compareTo(Integer.valueOf(p2.age));
     }
  }
}

比较程序首先比较两个名字,如果它们不相等,就返回比较结果,否则就返回比较两人年龄时的比较结果。

这段代码只是一个草稿:因为这个类是不可变的,你可以考虑为它构建一个单例,而不是为每次排序创建一个新实例。

使用Comparator,然后将对象放入Collection,然后Collections.sort();

class Person {

    String fname;
    String lname;
    int age;

    public Person() {
    }

    public int getAge() {
        return age;
    }

    public void setAge(int age) {
        this.age = age;
    }

    public String getFname() {
        return fname;
    }

    public void setFname(String fname) {
        this.fname = fname;
    }

    public String getLname() {
        return lname;
    }

    public void setLname(String lname) {
        this.lname = lname;
    }

    public Person(String fname, String lname, int age) {
        this.fname = fname;
        this.lname = lname;
        this.age = age;
    }

    @Override
    public String toString() {
        return fname + "," + lname + "," + age;
    }
}

public class Main{

    public static void main(String[] args) {
        List<Person> persons = new java.util.ArrayList<Person>();
        persons.add(new Person("abc3", "def3", 10));
        persons.add(new Person("abc2", "def2", 32));
        persons.add(new Person("abc1", "def1", 65));
        persons.add(new Person("abc4", "def4", 10));
        System.out.println(persons);
        Collections.sort(persons, new Comparator<Person>() {

            @Override
            public int compare(Person t, Person t1) {
                return t.getAge() - t1.getAge();
            }
        });
        System.out.println(persons);

    }
}
Arrays.sort(persons, new PersonComparator());



import java.util.Comparator;

public class PersonComparator implements Comparator<? extends Person> {

    @Override
    public int compare(Person o1, Person o2) {
        if(null == o1 || null == o2  || null == o1.getName() || null== o2.getName() ){
            throw new NullPointerException();
        }else{
            int nameComparisonResult = o1.getName().compareTo(o2.getName());
            if(0 == nameComparisonResult){
                return o1.getAge()-o2.getAge();
            }else{
                return nameComparisonResult;
            }
        }
    }
}


class Person{
    int age; String name;

    public int getAge() {
        return age;
    }

    public void setAge(int age) {
        this.age = age;
    }

    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }

}

升级版:

public class PersonComparator implements Comparator<? extends Person> {

   @Override
   public int compare(Person o1, Person o2) {

      int nameComparisonResult = o1.getName().compareToIgnoreCase(o2.getName());
      return 0 == nameComparisonResult?o1.getAge()-o2.getAge():nameComparisonResult;

   }
 }

使用Java 8 Streams方法,在getter上引用方法…

// Create a stream...
var sortedList = persons.stream()
    // sort it (does not sort the original list)...
    .sorted(Comparator.comparing(Person::getName)
                      .thenComparing(Person::getAge));
    // and collect to a new list
    .collect(Collectors.toList());

集合到数组ist也可以:

persons.stream()
    .sorted(Comparator.comparing(Person::getName)
                      .thenComparing(Person::getAge));
    .toArray(String[]::new);

Java 8 Lambda方法……

//Sorts the original list Lambda style
persons.sort((p1, p2) -> {
        if (p1.getName().compareTo(p2.getName()) == 0) {
            return p1.getAge().compareTo(p2.getAge());
        } else {
            return p1.getName().compareTo(p2.getName());
        } 
    });

最后……

// This syntax is similar to the Streams example above, but sorts the original list!!!
persons.sort(Comparator.comparing(Person::getName).thenComparing(Person::getAge));

您可以使用通用串行比较器按多个字段对集合进行排序。

import org.apache.commons.lang3.reflect.FieldUtils;
import java.util.Arrays;
import java.util.Comparator;
import java.util.List;

/**
* @author MaheshRPM
*/
public class SerialComparator<T> implements Comparator<T> {
List<String> sortingFields;

public SerialComparator(List<String> sortingFields) {
    this.sortingFields = sortingFields;
}

public SerialComparator(String... sortingFields) {
    this.sortingFields = Arrays.asList(sortingFields);
}

@Override
public int compare(T o1, T o2) {
    int result = 0;
    try {
        for (String sortingField : sortingFields) {
            if (result == 0) {
                Object value1 = FieldUtils.readField(o1, sortingField, true);
                Object value2 = FieldUtils.readField(o2, sortingField, true);
                if (value1 instanceof Comparable && value2 instanceof Comparable) {
                    Comparable comparable1 = (Comparable) value1;
                    Comparable comparable2 = (Comparable) value2;
                    result = comparable1.compareTo(comparable2);
                } else {
                    throw new RuntimeException("Cannot compare non Comparable fields. " + value1.getClass()
                            .getName() + " must implement Comparable<" + value1.getClass().getName() + ">");
                }
            } else {
                break;
            }
        }
    } catch (IllegalAccessException e) {
        throw new RuntimeException(e);
    }
    return result;
}
}