public interface Comparator<T>
接口里面的方法
int compare(T o1, T o2) o1 > o2 返回 1 o1 = o2 返回 0 o1 < o2 返回 -1 boolean equals(Object obj) 判断是否相等
其他方法：https://docs.oracle.com/javase/8/docs/api/java/util/Comparator.html
强行对某个对象 collection 进行整体排序 的比较函数。可以将 Comparator 传递给 sort 方法（如 Collections.sort 或 Arrays.sort），从而允许在排序顺序上实现精确控制。还可以使用 Comparator 来控制某些数据结构（如有序 set或有序映射）的顺序，或者为那些没有自然顺序的对象 collection 提供排序。
将数组中偶数排的后面
实现Comparator接口
class myComparator implements Comparator<Integer>{ public int compare(Integer a,Integer b){ return a%2==0?1:-1; } }
Comparator 传递给 sort 方法
package arrays1; import java.util.Arrays; import java.util.Comparator; class myComparator implements Comparator<Integer>{ public int compare(Integer a,Integer b){ return a%2==0?1:-1; } } public class myArray { public void mySort(){ Integer[] A = new Integer[]{2,0,345,234,12,34,23}; System.out.println(Arrays.toString(A)); Arrays.sort(A,new myComparator()); System.out.println(Arrays.toString(A)); } public static void main(String[] args){ new myArray().mySort(); } }
输出结果：
[2, 0, 345, 234, 12, 34, 23]
[23, 345, 2, 0, 234, 12, 34]
上面传递的是一个实例类对象
我们可以根据上节讲的内部类实现
package arrays1; import java.util.Arrays; import java.util.Comparator; public class myArray { class innerComparator implements Comparator<Integer>{ public int compare(Integer a,Integer b){ return a%2==0?1:-1; } } public void mySort(){ Integer[] A = new Integer[]{2,0,345,234,12,34,23}; System.out.println(Arrays.toString(A)); Arrays.sort(A,new innerComparator()); System.out.println(Arrays.toString(A)); } public static void main(String[] args){ new myArray().mySort(); } }
上面是成员内部类
也可以讲内部类写在方法中，
package arrays1; import java.util.Arrays; import java.util.Comparator; public class myArray { public void mySort(){ Integer[] A = new Integer[]{2,0,345,234,12,34,23}; System.out.println(Arrays.toString(A)); Arrays.sort(A,new Comparator<Integer>(){ public int compare(Integer a,Integer b){ return a%2==0?1:-1; } }); System.out.println(Arrays.toString(A)); } public static void main(String[] args){ new myArray().mySort(); } }
上面输出结果都一样
上面全部程序
package arrays1; import java.util.Arrays; import java.util.Comparator; class myComparator implements Comparator<Integer>{ public int compare(Integer a,Integer b){ return a%2==0?1:-1; } } public class myArray { class innerComparator implements Comparator<Integer>{ public int compare(Integer a,Integer b){ return b - a; } } public void mySort(){ Integer[] A = new Integer[]{2,0,345,234,12,34,23}; System.out.println(Arrays.toString(A)); // Arrays.sort(A,new myComparator()); // // System.out.println(Arrays.toString(A)); // Arrays.sort(A,new innerComparator()); // // System.out.println(Arrays.toString(A)); Arrays.sort(A,new Comparator<Integer>(){ public int compare(Integer a,Integer b){ return a%2==0?1:-1; } }); System.out.println(Arrays.toString(A)); } public static void main(String[] args){ new myArray().mySort(); } }
对人按照年龄排序
定义People类
class People{ int sex; int age; String name; People(int sex,int age,String name){ this.sex = sex; this.age = age; this.name = name; } public void setSex(int sex){ this.sex = sex; } public void setAge(int age){ this.age = age; } public void setName(String name){ this.name = name; } public int getSex() { return sex; } public int getAge() { return age; } public String getName() { return name; } public String toString(){ String p = "sex: "+sex+" age: "+ age+" name: "+ name+" "; return p; } }
实现Comparator接口，按照年龄排序，这里通过内部类实现的
public class myArray { class innerComparatorAge implements Comparator<People>{ public int compare(People a,People b){ // 按照年龄升序 return a.age - b.age; } } public void mySort(){ int N = 10; People[] A = new People[N]; Random rand = new Random(); for(int i = 0;i< N;i++){ int sex = rand.nextInt(2); int age = 10+ rand.nextInt(40); String name = ""+rand.nextInt(2000); A[i] = new People(sex,age,name); } System.out.println(Arrays.toString(A)); System.out.println("排序后："); Arrays.sort(A,new innerComparatorAge()); System.out.println(Arrays.toString(A)); } public static void main(String[] args){ new myArray().mySort(); } }
输出
[sex: 0 age: 23 name: 1067 , sex: 0 age: 16 name: 416 , sex: 1 age: 37 name: 465 , sex: 0 age: 13 name: 1667 , sex: 0 age: 46 name: 1698 , sex: 0 age: 13 name: 528 , sex: 1 age: 21 name: 1558 , sex: 0 age: 18 name: 1386 , sex: 1 age: 49 name: 249 , sex: 1 age: 34 name: 178 ] 排序后： [sex: 0 age: 13 name: 1667 , sex: 0 age: 13 name: 528 , sex: 0 age: 16 name: 416 , sex: 0 age: 18 name: 1386 , sex: 1 age: 21 name: 1558 , sex: 0 age: 23 name: 1067 , sex: 1 age: 34 name: 178 , sex: 1 age: 37 name: 465 , sex: 0 age: 46 name: 1698 , sex: 1 age: 49 name: 249 ]
当然也可以修改按照其他方式排序
按照性别排序，当性别相同的时候按照年龄排序
class innerComparatorSexAge implements Comparator<People>{ public int compare(People a,People b){ if(a.sex > b.sex) return 1; else if(a.sex < b.sex) return -1; else return a.age - b.age; } }
输出
[sex: 0 age: 43 name: 1284 , sex: 1 age: 11 name: 141 , sex: 0 age: 36 name: 1217 , sex: 0 age: 12 name: 1804 , sex: 0 age: 32 name: 1943 , sex: 0 age: 19 name: 1670 , sex: 1 age: 49 name: 656 , sex: 0 age: 36 name: 1349 , sex: 1 age: 13 name: 1542 , sex: 0 age: 18 name: 612 ] 排序后： [sex: 0 age: 12 name: 1804 , sex: 0 age: 18 name: 612 , sex: 0 age: 19 name: 1670 , sex: 0 age: 32 name: 1943 , sex: 0 age: 36 name: 1217 , sex: 0 age: 36 name: 1349 , sex: 0 age: 43 name: 1284 , sex: 1 age: 11 name: 141 , sex: 1 age: 13 name: 1542 , sex: 1 age: 49 name: 656 ]
programcreek 中整理的
实现Comparator 对Arrays , ArrayList , TreeSet ,TreeMap ,HashMap 排序
注意：对Map排序需要新建一个Map，将为排序的Map元素放入到新的Map中，这里是通过Key进行排序的
ArrayList
// Collections.sort List<ObjectName> list = new ArrayList<ObjectName>(); Collections.sort(list, new Comparator<ObjectName>() { public int compare(ObjectName o1, ObjectName o2) { return o1.toString().compareTo(o2.toString()); } });
Arrays
// Arrays.sort ObjectName[] arr = new ObjectName[10]; Arrays.sort(arr, new Comparator<ObjectName>() { public int compare(ObjectName o1, ObjectName o2) { return o1.toString().compareTo(o2.toString()); } });
TreeSet
// TreeSet Set<ObjectName> sortedSet = new TreeSet<ObjectName>(new Comparator<ObjectName>() { public int compare(ObjectName o1, ObjectName o2) { return o1.toString().compareTo(o2.toString()); } }); sortedSet.addAll(unsortedSet);
TreeMap
// TreeMap - using String.CASE_INSENSITIVE_ORDER which is a Comparator that orders Strings by compareToIgnoreCase Map<String, Integer> sortedMap = new TreeMap<String, Integer>(String.CASE_INSENSITIVE_ORDER); sortedMap.putAll(unsortedMap);
//TreeMap - In general, defined comparator Map<ObjectName, String> sortedMap = new TreeMap<ObjectName, String>(new Comparator<ObjectName>() { public int compare(ObjectName o1, ObjectName o2) { return o1.toString().compareTo(o2.toString()); } }); sortedMap.putAll(unsortedMap);
给个题目：