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用collection.sort（）方法對list集合排序

第一種是list中的對象實現Comparable接口，如下：?

/**? *?根據order對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());?}? }

?

測試一下：?

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>();?//此處add?user2再add?user1?list.add(user2);?list.add(user1);?Collections.sort(list);?for(User?u?:?list){?System.out.println(u.getName());?}?}? }

?

輸出結果如下?
a?
b?

第二種方法是根據Collections.sort重載方法來實現，例如：?

/**? *?根據order對User排序? */? public?class?User?{?//此處無需實現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;?}? }

?

主類中這樣寫即可：?

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());?}?}? }

?

輸出結果如下?
a?
b?
前者代碼結構簡單，但是只能根據固定的屬性排序，后者靈活，可以臨時指定排序項，但是代碼不夠簡潔

多字段的場合：?

Collections.sort(list,new?Comparator<User>(){?public?int?compare(User?arg0,?User?arg1)?{? //????????????第一次比較專業?int?i?=?arg0.getOrder().compareTo(arg1.getOrder()); //????????????如果專業相同則進行第二次比較?if(i==0){? //????????????????第二次比較?int?j=arg0.getXXX().compareTo(arg1.getXXX());? //????????????????如果學制相同則返回按年齡排序?if(j==0){?return?arg0.getCCC().compareTo(arg1.getCCC());?}?return?j;?}?return?i;?}?});

以下是另外一個例子?

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()?;?//按照工資升序? //return??arg0.getSalary()-arg1.getSalary()?;?按照工資降序? //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;? }

轉載于:https://my.oschina.net/u/858284/blog/267524

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