1、先来个简单的,上代码
import java.util.ArrayList;
import java.util.Collections;
import java.util.List;
public class sort {
public static void main(String[] args) {
List<Integer> list = new ArrayList<Integer>();
list.add(new Integer(5));
list.add(new Integer(13));
list.add(new Integer(4));
list.add(new Integer(9));
Collections.sort(list);
System.out.println(list.toString());
}
}
程序运行结果:
[4, 5, 9, 13],这种简单的排序直接按照自然顺序进行升序排列。
PS:jdk1.8中,list对象本身,也增加了实例方法sort(Comparator c),也可以直接进行排序,用法与Collections.sort()类似,不再赘述。
2、list参数类型相对复杂的排序
import java.util.ArrayList;
import java.util.Collections;
import java.util.List;
public class sort {
public static void main(String[] args) {
List<User> list = new ArrayList<User>();
list.add(new User("张三", 5));
list.add(new User("李四", 30));
list.add(new User("王五", 19));
list.add(new User("陈十七", 17)); // 陈十七永远十七岁
Collections.sort(list); // 按年龄排序
System.out.println(list.toString());
}
}
class User implements Comparable<User>{
private String name; //姓名
private int age; // 年龄
public User(String name, int age) {
this.name = name;
this.age = age;
}
// getter && setter
public String getName() {
return name;
}
public void setName(String name) {
this.name = name;
}
public int getAge() {
return age;
}
public void setAge(int age) {
this.age = age;
}
@Override
public String toString() {
return "User [name=" + name + ", age=" + age + "]";
}
@Override
public int compareTo(User user) { //重写Comparable接口的compareTo方法,
return this.age - user.getAge(); // 根据年龄升序排列,降序修改相减顺序即可
}
}
程序运行结果:根据年龄升序排列
[User [name=张三, age=5], User [name=陈十七, age=17], User [name=王五, age=19], User [name=李四, age=30]]
3、匿名内部类实现排序
public class sort {
public static void main(String[] args) {
List<User> list = new ArrayList<User>();
list.add(new User("张三", 5));
list.add(new User("李四", 30));
list.add(new User("王五", 19));
list.add(new User("陈十七", 17)); // 陈十七永远十七岁
Collections.sort(list, new Comparator<User>() {
@Override
public int compare(User u1, User u2) {
int diff = u1.getAge() - u2.getAge();
if (diff > 0) {
return 1;
}else if (diff < 0) {
return -1;
}
return 0; //相等为0
}
}); // 按年龄排序
System.out.println(list.toString());
}
}
运行结果:[User [name=张三, age=5], User [name=陈十七, age=17], User [name=王五, age=19], User [name=李四, age=30]]
根据以上,提取出一个公共的ListComparator:
public class ListComparator implements Comparator<Object> {
// 是否转化为Int之后再比较
private boolean isConvertInteger;
// 对哪个列进行排序
private String comparedProperty;
// 排序顺序,升序或者降序
private String sortBy;
public ListComparator(boolean isConvertInteger, String comparedProperty, String sortBy) {
super();
this.isConvertInteger = isConvertInteger;
this.comparedProperty = comparedProperty;
this.sortBy = sortBy;
}
public int compare(Object o1, Object o2) {
if (null != o1 && null != o2) {
try {
Object obj1 = getFieldValueByFieldName(comparedProperty, o1);
Object obj2 = getFieldValueByFieldName(comparedProperty, o2);
if (isConvertInteger) {
int num1;
int num2;
if (obj1 instanceof Integer) {
num1 = (Integer) obj1;
num2 = (Integer) obj2;
} else {
num1 = Integer.parseInt(obj1.toString());
num2 = Integer.parseInt(obj2.toString());
}
if ("desc".equalsIgnoreCase(sortBy)) {
return num2 - num1;
} else {
return num1 - num2;
}
} else {
if ("desc".equalsIgnoreCase(sortBy)) {
return obj2.toString().compareTo(obj1.toString());
} else {
return obj1.toString().compareTo(obj2.toString());
}
}
} catch (SecurityException e) {
e.printStackTrace();
} catch (IllegalArgumentException e) {
e.printStackTrace();
}
}
return 0/* 等于 */;
}
public static Object getFieldValueByFieldName(String fieldName, Object object) {
try {
Field field = object.getClass().getDeclaredField(fieldName);
// 对private的属性的访问
field.setAccessible(true);
return field.get(object);
} catch (Exception e) {
e.printStackTrace();
return null;
}
}
}