有的时候需要对数组里的element进行排序。当然可以自己编写合适的排序方法但既然java包里有自带的Arrays.sort排序方法在数组元素比较少 有的时候需要对数组里的element进行排序。当然可
有的时候需要对数组里的element进行排序。当然可以自己编写合适的排序方法但既然java包里有自带的Arrays.sort排序方法在数组元素比较少
有的时候需要对数组里的element进行排序。当然可以自己编写合适的排序方法但既然java包里有自带的Arrays.sort排序方法在 数组元素比较少的时候为何不用
Sorting an Array 1. 数字排序 int[] intArray new int[] { 4, 1, 3, -23 };
Arrays.sort(intArray);
输出 [-23, 1, 3, 4]
2. 字符串排序先大写后小写 String[] strArray new String[] { "z", "a", "C" };
Arrays.sort(strArray);
输出 [C, a, z]
3. 严格按字母表顺序排序也就是忽略大小写排序 Case-insensitive sort
Arrays.sort(strArray, String.CASE_INSENSITIVE_ORDER);
输出 [a, C, z]
4. 反向排序 Reverse-order sort
Arrays.sort(strArray, Collections.reverseOrder());
输出[z, a, C]
5. 忽略大小写反向排序 Case-insensitive reverse-order sort
Arrays.sort(strArray, String.CASE_INSENSITIVE_ORDER);
Collections.reverse(Arrays.asList(strArray));
输出 [z, C, a]
java初学者最常见的错误思想就是试图去写一些方法来完成数组的排序功能其实数组排序功能在java的api里面早已实现我们没有 必要去重复制造轮子。
Arrays类有一个静态方法sort,利用这个方法我们可以传入我们要排序的数组进去排序因为我们传入的是一个数组的引用所以排序完成的 结果也通过这个引用的来更改数组.对于整数、字符串排序jdk提供了默认的实现如果要对一个对象数组排序则要自己实现 java.util.Comparator接口。
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package com.gjh.gee.arrays; import java.util.Arrays; public class ArraySortDemo { public void sortIntArray() { int[] arrayToSort new int[] { 48, 5, 89, 80, 81, 23, 45, 16, 2 }; System.out.println("排序前"); for (int i 0; i < arrayToSort.length; i) System.out.println(arrayToSort[i]); // 调用数组的静态排序方法sort Arrays.sort(arrayToSort); System.out.println("排序后"); for (int i 0; i < arrayToSort.length; i) System.out.println(arrayToSort[i]); } public void sortStringArray() { String[] arrayToSort new String[] { "Oscar", "Charlie", "Ryan", "Adam", "David" }; System.out.println("排序前"); for (int i 0; i < arrayToSort.length; i) System.out.println(arrayToSort[i]); System.out.println("排序后"); // 调用数组的静态排序方法sort Arrays.sort(arrayToSort); for (int i 0; i < arrayToSort.length; i) System.out.println(arrayToSort[i]); } public void sortObjectArray() { Dog o1 new Dog("dog1", 1); Dog o2 new Dog("dog2", 4); Dog o3 new Dog("dog3", 5); Dog o4 new Dog("dog4", 2); Dog o5 new Dog("dog5", 3); Dog[] dogs new Dog[] { o1, o2, o3, o4, o5 }; System.out.println("排序前"); for (int i 0; i < dogs.length; i) { Dog dog dogs[i]; System.out.println(dog.getName()); } Arrays.sort(dogs, new ByWeightComparator()); System.out.println("排序后"); for (int i 0; i < dogs.length; i) { Dog dog dogs[i]; System.out.println(dog.getName()); } } public static void main(String[] args) { ArraySortDemo t new ArraySortDemo(); t.sortIntArray(); t.sortStringArray(); t.sortObjectArray(); } }
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package com.gjh.gee.arrays; public class Dog { private String name; private int weight; public Dog(String name, int weight) { this.setName(name); this.weight weight; } public int getWeight() { return weight; } public void setWeight(int weight) { this.weight weight; } public void setName(String name) { this.name name; } public String getName() { return name; } }
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package com.gjh.gee.arrays; import java.util.Comparator; public class ByWeightComparator implements Comparator { public final int compare(Object pFirst, Object pSecond) { int aFirstWeight ((Dog) pFirst).getWeight(); int aSecondWeight ((Dog) pSecond).getWeight(); int diff aFirstWeight - aSecondWeight; if (diff > 0) return 1; if (diff < 0) return -1; else return 0; } }
下面补充一个Collections.sort排序原理和Arrays.sort差不多。
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//一个POJO例子 class User { String name; String age; public User(String name,String age){ this.namename; this.ageage; } public String getAge() { return age; } public void setAge(String age) { this.age age; } public String getName() { return name; } public void setName(String name) { this.name name; } } //具体的比较类实现Comparator接口 import java.util.Comparator; import java.util.List; import java.util.ArrayList; import java.util.Collections; public class ComparatorUser implements Comparator{ public int compare(Object arg0, Object arg1) { User user0(User)arg0; User user1(User)arg1; //首先比较年龄如果年龄相同则比较名字 int flaguser0.getAge().compareTo(user1.getAge()); if(flag0){ return user0.getName().compareTo(user1.getName()); }else{ return flag; } } } //测试类 public class SortTest { public static void main(String[] args){ List userlistnew ArrayList(); userlist.add(new User("dd","4")); userlist.add(new User("aa","1")); userlist.add(new User("ee","5")); userlist.add(new User("bb","2")); userlist.add(new User("ff","5")); userlist.add(new User("cc","3")); userlist.add(new User("gg","6")); ComparatorUser comparatornew ComparatorUser(); Collections.sort(userlist, comparator); for (int i0;i User user_temp(User)userlist.get(i); System.out.println(user_temp.getAge()","user_temp.getName()); } } }
//首先年龄排序如果年龄相同则按名字排序 结果: 1, aa 2, bb 3, cc 4, dd 5, ee //注意:同样是5岁的人则比较名字(ee,ff)然后排序 5, ff 6, gg