首先讲一下Comparable接口和Comparator接口,以及他们之间的差异。有助于Collections.sort()方法的使用。请参考
1.Comparable自然规则排序
//在自定义类Student里面实现Comparable接口,并重写抽象方法compareTo(User u);
//Collections.sort(集合);
实例:
public static void main(String[] args) {
List<Integer> nums = new ArrayList<Integer>();
nums.add(3);
nums.add(5);
nums.add(1);
nums.add(0);
System.out.println(nums);
Collections.sort(nums);
System.out.println(nums);
}
输出结果:
[3, 5, 1, 0]
[0, 1, 3, 5]
稍微复杂的List里面放一个复杂的对象
public class ListTest {
public static void main(String[] args) {
List<User> list = new ArrayList<User>();
User u1 = new User(1,"张三丰");
User u2 = new User(2,"王重阳");
User u3 = new User(3,"郭靖");
User u4 = new User(4,"1");
User u5 = new User(5,"awm");
list.add(u1);
list.add(u2);
list.add(u3);
list.add(u4);
list.add(u5);
for(User u : list){
System.out.print(u.getAge() + "-" +u.getName() + " ");
}
System.out.println();
Collections.sort(list);
for(User u : list){
System.out.print(u.getAge() + "-" +u.getName() + " ");
}
}
}
class User implements Comparable<User> {
//省略构造器及get/set方法
@Override
public int compareTo(User o) {
return this.name.compareTo(o.getName());
}
}
输出结果:
1-张三丰 2-王重阳 3-郭靖 4-1 5-awm
4-1 5-awm 1-张三丰 2-王重阳 3-郭靖
很明显咱们要求的按name中文排序是没有达到的,咱们再做下调整,如下例
public class ListTest {
public static void main(String[] args) {
// TODO Auto-generated method stub
List<User> list = new ArrayList<User>();
User u1 = new User(1,"张三丰");
User u2 = new User(2,"王重阳");
User u3 = new User(3,"郭靖");
User u4 = new User(4,"1");
User u5 = new User(5,"awm");
list.add(u1);
list.add(u2);
list.add(u3);
list.add(u4);
list.add(u5);
for(User u : list){
System.out.print(u.getAge() + "-" +u.getName() + " ");
}
System.out.println();
Collections.sort(list);
for(User u : list){
System.out.print(u.getAge() + "-" +u.getName() + " ");
}
}
}
class User implements Comparable<User> {
Collator collator = Collator.getInstance(java.util.Locale.CHINA);
//省略属性及get/set方法
@Override
public int compareTo(User o) {
// TODO Auto-generated method stub
return collator.compare(this.name, o.getName());
}
}
输出结果:
1-张三丰 2-王重阳 3-郭靖 4-1 5-awm
4-1 5-awm 3-郭靖 2-王重阳 1-张三丰
符合排序要求
我们会发现sort(List<T>)方法中List中的T必须实现Comparable<T>接口,然后实现compareTo()方法,该方法的返回值0代表相等,整数表示大于,负数表示小于;为什么在简单例子中没有看到实现Comparable接口呢?是因为Integer类其实自己已经实现了Comparable接口,Java已经给我们做好了。
2.Comparator专门规则排序(l临时排序)
//新建一个实现了Comparator接口的类,并重写抽象方法compare(User u1, User u2);
//Collections.sort(集合,实现了Comparator接口的类的实例化对象);
Collections提供的第二种排序方法sort(List<T> list, Comparator<? super T> c)
先看例子:
public class ListTest {
public static void main(String[] args) {
// TODO Auto-generated method stub
List<User> list = new ArrayList<User>();
User u1 = new User(1,"张三丰");
User u2 = new User(2,"王重阳");
User u3 = new User(3,"郭靖");
User u4 = new User(4,"1");
User u5 = new User(5,"awm");
list.add(u1);
list.add(u2);
list.add(u3);
list.add(u4);
list.add(u5);
for(User u : list){
System.out.print(u.getAge() + "-" +u.getName() + " ");
}
System.out.println();
Collections.sort(list,new User());
for(User u : list){
System.out.print(u.getAge() + "-" +u.getName() + " ");
}
}
}
class User implements Comparator<User> {
Collator collator = Collator.getInstance(java.util.Locale.CHINA);
//省略属性及get/set方法
@Override
public int compare(User o1, User o2) {
// TODO Auto-generated method stub
return collator.compare(o1.getName(), o2.getName());
}
}
输出结果:
1-张三丰 2-王重阳 3-郭靖 4-1 5-awm
4-1 5-awm 3-郭靖 2-王重阳 1-张三丰
符合排序要求
从上面的例子我们可以看出Students类没有实现Comparable<T>接口,只是在sort()方法中多传入一个参数,只不过该参数是一个接口我们需要实现其compare方法。
以上两种均可实现按集合对象属性首字母或者说是拼音排序,仅供参考。