Java 8 Lambda缩短了排序。

Collections.sort(stdList, (o1, o2) -> o1.getName().compareTo(o2.getName()));

1.8以来的新功能是一个List.sort()方法，而不是使用Collection.sort() 直接调用mylistcontainer。sort()

下面是一个演示List.sort()特性的代码片段:

List<Fruit> fruits = new ArrayList<Fruit>();
fruits.add(new Fruit("Kiwi","green",40));
fruits.add(new Fruit("Banana","yellow",100));
fruits.add(new Fruit("Apple","mixed green,red",120));
fruits.add(new Fruit("Cherry","red",10));

// a) using an existing compareto() method
fruits.sort((Fruit f1,Fruit f2) -> f1.getFruitName().compareTo(f2.getFruitName()));
System.out.println("Using String.compareTo(): " + fruits);
//Using String.compareTo(): [Apple is: mixed green,red, Banana is: yellow, Cherry is: red, Kiwi is: green]

// b) Using a comparable class
fruits.sort((Fruit f1,Fruit f2) -> f1.compareTo(f2));  
System.out.println("Using a Comparable Fruit class (sort by color): " + fruits);
// Using a Comparable Fruit class (sort by color): [Kiwi is green, Apple is: mixed green,red, Cherry is: red, Banana is: yellow]

Fruit类是:

public class Fruit implements Comparable<Fruit>
{
    private String name;
    private String color;
    private int quantity;

    public Fruit(String name,String color,int quantity)
    { this.name = name; this.color = color; this.quantity = quantity; }

    public String getFruitName() { return name; }        
    public String getColor() { return color; }  
    public int getQuantity() { return quantity; }

    @Override public final int compareTo(Fruit f) // sorting the color
    {
        return this.color.compareTo(f.color);
    }     
    @Override public String toString()
    {   
        return (name + " is: " + color);
    }
} // end of Fruit class   

我发现这些答案大部分(如果不是全部的话)依赖于底层类(Object)来实现类似的接口或具有类似的helper接口。

没有我的解决方案!下面的代码允许您通过知道对象的字符串名称来比较对象的字段。您可以很容易地修改它，不使用名称，但随后需要公开它或构造一个想要进行比较的对象。

Collections.sort(anArrayListOfSomeObjectPerhapsUsersOrSomething, new ReflectiveComparator(). new ListComparator("name"));

public class ReflectiveComparator {
    public class FieldComparator implements Comparator<Object> {
        private String fieldName;

        public FieldComparator(String fieldName){
            this.fieldName = fieldName;
        }

        @SuppressWarnings({ "unchecked", "rawtypes" })
        @Override
        public int compare(Object object1, Object object2) {
            try {
                Field field = object1.getClass().getDeclaredField(fieldName);
                field.setAccessible(true);

                Comparable object1FieldValue = (Comparable) field.get(object1);
                Comparable object2FieldValue = (Comparable) field.get(object2);

                return object1FieldValue.compareTo(object2FieldValue);
            }catch (Exception e){}

            return 0;
        }
    }

    public class ListComparator implements Comparator<Object> {
        private String fieldName;

        public ListComparator(String fieldName) {
            this.fieldName = fieldName;
        }

        @SuppressWarnings({ "unchecked", "rawtypes" })
        @Override
        public int compare(Object object1, Object object2) {
            try {
                Field field = object1.getClass().getDeclaredField(fieldName);
                field.setAccessible(true);
                Comparable o1FieldValue = (Comparable) field.get(object1);
                Comparable o2FieldValue = (Comparable) field.get(object2);

                if (o1FieldValue == null){ return -1;}
                if (o2FieldValue == null){ return 1;}
                return o1FieldValue.compareTo(o2FieldValue);
            } catch (NoSuchFieldException e) {
                throw new IllegalStateException("Field doesn't exist", e);
            } catch (IllegalAccessException e) {
                throw new IllegalStateException("Field inaccessible", e);
            }
        }
    }
}

你的customComparator类必须实现java.util.Comparator才能被使用。 它还必须覆盖compare() AND equals()

compare()必须回答这个问题:对象1是否小于、等于或大于对象2?

完整文档:http://java.sun.com/j2se/1.5.0/docs/api/java/util/Comparator.html

具有自然排序顺序的类(例如类Number)应该实现Comparable接口，而没有自然排序顺序的类(例如类Chair)应该提供Comparator(或匿名Comparator类)。

两个例子:

public class Number implements Comparable<Number> {
    private int value;

    public Number(int value) { this.value = value; }
    public int compareTo(Number anotherInstance) {
        return this.value - anotherInstance.value;
    }
}

public class Chair {
    private int weight;
    private int height;

    public Chair(int weight, int height) {
        this.weight = weight;
        this.height = height;
    }
    /* Omitting getters and setters */
}
class ChairWeightComparator implements Comparator<Chair> {
    public int compare(Chair chair1, Chair chair2) {
        return chair1.getWeight() - chair2.getWeight();
    }
}
class ChairHeightComparator implements Comparator<Chair> {
    public int compare(Chair chair1, Chair chair2) {
        return chair1.getHeight() - chair2.getHeight();
    }
}

用法:

List<Number> numbers = new ArrayList<Number>();
...
Collections.sort(numbers);

List<Chair> chairs = new ArrayList<Chair>();
// Sort by weight:
Collections.sort(chairs, new ChairWeightComparator());
// Sort by height:
Collections.sort(chairs, new ChairHeightComparator());

// You can also create anonymous comparators;
// Sort by color:
Collections.sort(chairs, new Comparator<Chair>() {
    public int compare(Chair chair1, Chair chair2) {
        ...
    }
});

使用java-8流api，你可以对数组列表进行排序:

 Comparator<Person> birthdayComparator = Comparator.comparing(Person::getBirthday);
 List<Person> sortedList = list.stream().sorted(birthdayComparator).collect(toList());