最近正好用到Comparator，發(fā)現(xiàn)能對(duì)不同類型的對(duì)象進(jìn)行排序(當(dāng)然排序依據(jù)還是基本類型)，也不用自己實(shí)現(xiàn)排序算法，用起來很方便，所以簡(jiǎn)單記錄一下。

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Interface Comparator<T>對(duì)任意類型集合對(duì)象進(jìn)行整體排序，排序時(shí)將此接口的實(shí)現(xiàn)傳遞給Collections.sort方法或者Arrays.sort方法排序。實(shí)現(xiàn)int compare(T o1, T o2);方法，返回正數(shù)，零，負(fù)數(shù)各代表大于，等于，小于。具體看代碼。

簡(jiǎn)單例子：

public class Test {PRivate final class CompareName implements Comparator<Milan> {boolean is_Ascend;public CompareName(boolean b) {// TODO Auto-generated constructor stubis_Ascend = b;}@Overridepublic int compare(Milan o1, Milan o2) {// TODO Auto-generated method stubif (is_Ascend)return o1.p_Name.compareTo(o2.p_Name);elsereturn o2.p_Name.compareTo(o1.p_Name);}}private final class CompareId implements Comparator<Milan> {boolean is_Ascend;public CompareId(boolean b) {// TODO Auto-generated constructor stubis_Ascend = b;}@Overridepublic int compare(Milan o1, Milan o2) {// TODO Auto-generated method stubint a, b;if (is_Ascend) {a = o1.p_Id;b = o2.p_Id;} else {a = o2.p_Id;b = o1.p_Id;}if (a > b)return 1;else if (a == b)return 0;elsereturn -1;}}public static void main(String[] args) {Test t = new Test();Milan p1 = new Milan(1, "Dida");Milan p2 = new Milan(2, "Cafu");Milan p3 = new Milan(3, "Maldini");Milan P4 = new Milan(6, "Baresi");Milan p5 = new Milan(9, "Inzaghi");Milan P6 = new Milan(10, "Costa");List<Milan> mList = new ArrayList<Milan>();mList.add(p1);mList.add(P6);mList.add(P4);mList.add(p2);mList.add(p5);mList.add(p3);System.out.println("初始順序");System.out.println("姓名|號(hào)碼");for (Milan p : mList) {System.out.println(p.p_Name + "|" + p.p_Id);}System.out.println();System.out.println("對(duì)號(hào)碼降序");System.out.println("姓名|號(hào)碼");Collections.sort(mList, t.new CompareId(false));for (Milan p : mList) {System.out.println(p.p_Name + "|" + p.p_Id);}System.out.println();System.out.println("對(duì)姓名升序");System.out.println("姓名|號(hào)碼");Collections.sort(mList, t.new CompareName(true));for (Milan p : mList) {System.out.println(p.p_Name + "|" + p.p_Id);}}}

輸出結(jié)果：

初始順序姓名?|?號(hào)碼Dida?|?1Costa?|?10Baresi?|?6Cafu?|?2Inzaghi?|?9Maldini?|?3

對(duì)號(hào)碼降序姓名?|?號(hào)碼Costa?|?10Inzaghi?|?9Baresi?|?6Maldini?|?3Cafu?|?2Dida?|?1

對(duì)姓名升序姓名?|?號(hào)碼Baresi?|?6Cafu?|?2Costa?|?10Dida?|?1Inzaghi?|?9Maldini?|?3

sort方法第一個(gè)參數(shù)是一個(gè)list對(duì)象，排序結(jié)束后的結(jié)果就繼續(xù)保存在這個(gè)list中，可以直接使用。

附上文檔，不用再去查了

public interface Comparator<T>

A comparison function, which imposes a total ordering on some collection of objects. Comparators can be passed to a sort method (such as Collections.sort or Arrays.sort) to allow precise control over the sort order. Comparators can also be used to control the order of certain data structures (such as sorted sets or sorted maps), or to provide an ordering for collections of objects that don't have a natural ordering.The ordering imposed by a comparator c on a set of elements S is said to be consistent with equals if and only if c.compare(e1, e2)==0 has the same boolean value as e1.equals(e2) for every e1 and e2 in S.Caution should be exercised when using a comparator capable of imposing an ordering inconsistent with equals to order a sorted set (or sorted map). Suppose a sorted set (or sorted map) with an explicit comparator c is used with elements (or keys) drawn from a set S. If the ordering imposed by c on S is inconsistent with equals, the sorted set (or sorted map) will behave "strangely." In particular the sorted set (or sorted map) will violate the general contract for set (or map), which is defined in terms of equals.For example, suppose one adds two elements a and b such that (a.equals(b) && c.compare(a, b) != 0) to an empty TreeSet with comparator c. The second add Operation will return true (and the size of the tree set will increase) because a and b are not equivalent from the tree set's perspective, even though this is contrary to the specification of the Set.add method.Note: It is generally a good idea for comparators to also implement java.io.Serializable, as they may be used as ordering methods in serializable data structures (like TreeSet, TreeMap). In order for the data structure to serialize successfully, the comparator (if provided) must implement Serializable.For the mathematically inclined, the relation that defines the imposed ordering that a given comparator c imposes on a given set of objects S is:       {(x, y) such that c.compare(x, y) <= 0}.The quotient for this total order is:       {(x, y) such that c.compare(x, y) == 0}.It follows immediately from the contract for compare that the quotient is an equivalence relation on S, and that the imposed ordering is a total order on S. When we say that the ordering imposed by c on S is consistent with equals, we mean that the quotient for the ordering is the equivalence relation defined by the objects' equals(Object) method(s):     {(x, y) such that x.equals(y)}.Unlike Comparable, a comparator may optionally permit comparison of null arguments, while maintaining the requirements for an equivalence relation.

int compare(T o1, T o2)

Compares its two arguments for order. Returns a negative integer, zero, or a positive integer as the first argument is less than, equal to, or greater than the second.In the foregoing description, the notation sgn(expression) designates the mathematical signum function, which is defined to return one of -1, 0, or 1 according to whether the value of expression is negative, zero or positive.The implementor must ensure that sgn(compare(x, y)) == -sgn(compare(y, x)) for all x and y. (This implies that compare(x, y) must throw an exception if and only if compare(y, x) throws an exception.)The implementor must also ensure that the relation is transitive: ((compare(x, y)>0) && (compare(y, z)>0)) implies compare(x, z)>0.Finally, the implementor must ensure that compare(x, y)==0 implies that sgn(compare(x, z))==sgn(compare(y, z)) for all z.It is generally the case, but not strictly required that (compare(x, y)==0) == (x.equals(y)). Generally speaking, any comparator that violates this condition should clearly indicate this fact. The recommended language is "Note: this comparator imposes orderings that are inconsistent with equals."Parameters:o1 - the first object to be compared.o2 - the second object to be compared.Returns:a negative integer, zero, or a positive integer as the first argument is less than, equal to, or greater than the second.

boolean equals(Object obj)

Indicates whether some other object is "equal to" this comparator. This method must obey the general contract of Object.equals(Object). Additionally, this method can return true only if the specified object is also a comparator and it imposes the same ordering as this comparator. Thus, comp1.equals(comp2) implies that sgn(comp1.compare(o1, o2))==sgn(comp2.compare(o1, o2)) for every object reference o1 and o2.Note that it is always safe not to override Object.equals(Object). However, overriding this method may, in some cases, improve performance by allowing programs to determine that two distinct comparators impose the same order.Overrides:equals in class ObjectParameters:obj - the reference object with which to compare.Returns:true only if the specified object is also a comparator and it imposes the same ordering as this comparator.

public static <T> void sort(List<T> list, Comparator<? super T> c)

Sorts the specified list according to the order induced by the specified comparator. All elements in the list must be mutually comparable using the specified comparator (that is, c.compare(e1, e2) must not throw a ClassCastException for any elements e1 and e2 in the list).This sort is guaranteed to be stable: equal elements will not be reordered as a result of the sort.The sorting algorithm is a modified mergesort (in which the merge is omitted if the highest element in the low sublist is less than the lowest element in the high sublist). This algorithm offers guaranteed n log(n) performance. The specified list must be modifiable, but need not be resizable. This implementation dumps the specified list into an array, sorts the array, and iterates over the list resetting each element from the corresponding position in the array. This avoids the n2 log(n) performance that would result from attempting to sort a linked list in place.Parameters:list - the list to be sorted.c - the comparator to determine the order of the list. A null value indicates that the elements' natural ordering should be used.