用collection.sort（）方法对list集合排序

/** * 根据order对User排序 */ public class User implements Comparable<User>{ private String name; private Integer order; public String getName() { return name; } public void setName(String name) { this.name = name; } public Integer getOrder() { return order; } public void setOrder(Integer order) { this.order = order; } public int compareTo(User arg0) { return this.getOrder().compareTo(arg0.getOrder()); } }

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测试一下：public class Test{ public static void main(String[] args) { User user1 = new User(); user1.setName("a"); user1.setOrder(1); User user2 = new User(); user2.setName("b"); user2.setOrder(2); List<User> list = new ArrayList<User>(); //此处add user2再add user1 list.add(user2); list.add(user1); Collections.sort(list); for(User u : list){ System.out.println(u.getName()); } } }

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输出结果如下/** * 根据order对User排序 */ public class User { //此处无需实现Comparable接口 private String name; private Integer order; public String getName() { return name; } public void setName(String name) { this.name = name; } public Integer getOrder() { return order; } public void setOrder(Integer order) { this.order = order; } }

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主类中这样写即可：public class Test{ public static void main(String[] args) { User user1 = new User(); user1.setName("a"); user1.setOrder(1); User user2 = new User(); user2.setName("b"); user2.setOrder(2); List<User> list = new ArrayList<User>(); list.add(user2); list.add(user1); Collections.sort(list,new Comparator<User>(){ public int compare(User arg0, User arg1) { return arg0.getOrder().compareTo(arg1.getOrder()); } }); for(User u : list){ System.out.println(u.getName()); } } }

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输出结果如下?
a?
b?
前者代码结构简单，但是只能根据固定的属性排序，后者灵活，可以临时指定排序项，但是代码不够简洁

多字段的场合：?
Collections.sort(list,new Comparator<User>(){?
??????????? public int compare(User arg0, User arg1) {?
//??????????? 第一次比较专业?
??????????????? int i = arg0.getOrder().compareTo(arg1.getOrder());

//??????????? 如果专业相同则进行第二次比较?
??????????? if(i==0){?
//??????????????? 第二次比较?
??????????????? int j=arg0.getXXX().compareTo(arg1.getXXX());?
//??????????????? 如果学制相同则返回按年龄排序?
??????????????? if(j==0){?
??????????????????? return arg0.getCCC().compareTo(arg1.getCCC());?
??????????????? }?
??????????????? return j;?
??????????? }?
??????????? return i;?
??????????? }?
??????? });

以下是另外一个例子?
package test;

import java.util.ArrayList;?
import java.util.Collections;?
import java.util.Comparator;

public class ArrayListTest {?
public static void main(String[] args) {?
ArrayList<Exmployee> arrayList? = new ArrayList<Exmployee>() ;?
arrayList.add(new Exmployee("zengqiang",new Integer(5000))) ;?
arrayList.add(new Exmployee("zengmin",new Integer(4000))) ;?
arrayList.add(new Exmployee("liuxiaojuan",new Integer(4200))) ;?
arrayList.add(new Exmployee("giuming",new Integer(2200))) ;?
Collections.sort(arrayList, new Comparator<Exmployee>(){?
public int compare(Exmployee arg0, Exmployee arg1) {?
return? arg1.getSalary()-arg0.getSalary() ; //按照工资升序?
//return? arg0.getSalary()-arg1.getSalary() ; 按照工资降序?
//return arg0.getName().compareTo(arg1.getName()) ; 按照姓名升序?
??????????? }?
});?
for(Exmployee e:arrayList)?
System.out.println(e.getName()+"'s salary is "+e.getSalary()) ;?
}

}

class Exmployee {?
public Exmployee(String name, int salary) {?
this.name = name ;?
this.salary = salary ;?
}

private String name;

public String getName() {?
return name;?
}

public void setName(String name) {?
this.name = name;?
}

public int getSalary() {?
return salary;?
}

public void setSalary(int salary) {?
this.salary = salary;?
}

private int salary;?
}

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