排序Java集合對象基於一個領域它

Question

我有以下的集合：

Collection<AgentSummaryDTO> agentDtoList = new ArrayList<AgentSummaryDTO>(); 

凡AgentSummaryDTO看起來是這樣的：

public class AgentSummaryDTO implements Serializable { 
    private Long id; 
    private String agentName; 
    private String agentCode; 
    private String status; 
    private Date createdDate; 
    private Integer customerCount; 
} 

現在我要進行排序基於集合agentDtoListcustomerCount字段，該如何實現？

Answer 1

這裏是我的 「1liner」：

Collections.sort(agentDtoList, new Comparator<AgentSummaryDTO>(){ 
    public int compare(AgentSummaryDTO o1, AgentSummaryDTO o2){ 
     return o1.getCustomerCount() - o2.getCustomerCount(); 
    } 
}); 

更新的Java 8： 爲int數據類型

Collections.sort(agentDtoList, (o1, o2) -> o1.getCustomerCount() - o2.getCustomerCount()); 

字符串數據類型（如註釋）

Collections.sort(list, (o1, o2) -> (o1.getAgentName().compareTo(o2.getAgentName()))); 

..他預計gette [R AgentSummaryDTO.getCustomerCount()

Answer 2

查看Comparator和Collections類。

一個簡單的方法是在AgentSummaryDTO中實現Comparable接口，然後將該列表傳遞給Collections.sort()。

如果您不能編輯AgentSummaryDTO，你需要一個比較如下所示：How to sort a List<Object> alphabetically using Object name field

Answer 3

看一看下面的代碼。

package test; 

import java.io.Serializable; 
import java.util.ArrayList; 
import java.util.Collections; 
import java.util.Date; 
import java.util.List; 

public class AgentSummary { 
    private Long id; 
    private String agentName; 
    private String agentCode; 
    private String status; 
    private Date createdDate; 
    private Integer customerCount; 

    /** 
    * @param args 
    */ 
    public static void main(String[] args) { 
     // TODO Auto-generated method stub 

     List<AgentSummaryDTO> agentSummary = new ArrayList<AgentSummaryDTO>(); 
     for (int j = 0; j < 10; j++) { 
      agentSummary.add(new AgentSummaryDTO(j)); 
     } 
     Collections.sort(agentSummary); 

     for (AgentSummaryDTO obj : agentSummary) { 
      System.out.println("File " + obj.getCustomerCount()); 
     } 

    } 

} 

class AgentSummaryDTO implements Serializable, Comparable<AgentSummaryDTO> { 

    private Long id; 
    private String agentName; 
    private String agentCode; 
    private String status; 
    private Date createdDate; 
    private Integer customerCount; 

    AgentSummaryDTO() { 
     customerCount = null; 
    } 

    AgentSummaryDTO(int customerCount) { 
     this.customerCount = customerCount; 
    } 

    /** 
    * @return the id 
    */ 
    public Long getId() { 
     return id; 
    } 

    /** 
    * @param id 
    *   the id to set 
    */ 
    public void setId(Long id) { 
     this.id = id; 
    } 

    /** 
    * @return the agentName 
    */ 
    public String getAgentName() { 
     return agentName; 
    } 

    /** 
    * @param agentName 
    *   the agentName to set 
    */ 
    public void setAgentName(String agentName) { 
     this.agentName = agentName; 
    } 

    /** 
    * @return the agentCode 
    */ 
    public String getAgentCode() { 
     return agentCode; 
    } 

    /** 
    * @param agentCode 
    *   the agentCode to set 
    */ 
    public void setAgentCode(String agentCode) { 
     this.agentCode = agentCode; 
    } 

    /** 
    * @return the status 
    */ 
    public String getStatus() { 
     return status; 
    } 

    /** 
    * @param status 
    *   the status to set 
    */ 
    public void setStatus(String status) { 
     this.status = status; 
    } 

    /** 
    * @return the createdDate 
    */ 
    public Date getCreatedDate() { 
     return createdDate; 
    } 

    /** 
    * @param createdDate 
    *   the createdDate to set 
    */ 
    public void setCreatedDate(Date createdDate) { 
     this.createdDate = createdDate; 
    } 

    /** 
    * @return the customerCount 
    */ 
    public Integer getCustomerCount() { 
     return customerCount; 
    } 

    /** 
    * @param customerCount 
    *   the customerCount to set 
    */ 
    public void setCustomerCount(Integer customerCount) { 
     this.customerCount = customerCount; 
    } 

    @Override 
    public int compareTo(AgentSummaryDTO arg0) { 

     if (this.customerCount > arg0.customerCount) 
      return 0; 
     else 
      return 1; 
    } 

} 

Answer 4

的answer by Jiri Kremser甚至可以進一步簡化，這真的是做了完整的Java 8路：

Collections.sort(agentDtoList, Comparator.comparing(AgentSummaryDTO::getCustomerCount)); 

這只是由整型字段進行比較，並且效果很好，因爲Integer工具Comparable。

一個更清潔的解決方案可能是使用內置的comparingInt()方法：

sort(agentDtoList, comparingInt(AgentSummaryDTO::getCustomerCount)); 

Answer 5

UPDATE：

Collections.sort(agentDtoList, Comparator.comparingInt(AgentSummaryDTO::getCustomerCount)); 

當然，這可以通過靜態導入sort和comparingInt表示更短對於Java 8它的工作

Collections.sort(agentDtoList, (o1, o2) -> o1.getCustomerCount() - o2.getCustomerCount());