如何在java中对arraylist进行排序

Question

基本上可以通过以下方式进行排序:

Collections.sort(列表);

但我的情况有点不同.我有一个包含以下对象的List.

示例代码1:

public class GetTraders {
    private String getTraderLegalName;
    private String businessName;
    private Object status;

    public GetTraders(String getTraderLegalName, String businessName, String status) {
        this.getTraderLegalName=getTraderLegalName;
        this.businessName=businessName;
        this.status=status;
    }

我有一个课程,它将为以上列表提供如下价值:

public Class getResult {
    List<GetTraders> traders=new ArrayList<GetTraders>();
    public void valueGivenByuser(String legal,String business,Object status)throws Exception {
        GetTraders trade=new GetTraders(legal,business,status);
        traders.add(trade); //Adding value to arrayList
    }
}

这里的问题是,一旦我在交易者arraylist中添加了所有值,我需要排序并显示为输出.我尝试使用collections.sort()但它显示了编译器异常.

Answer 1

如果仔细查看Collections API,您会看到有两种选择:

1)让你的GetTraders类实现Comparable接口并调用

public static <T extends Comparable<? super T>> void sort(List<T> list)

2)为GetTraders类创建一个新的Comparator并调用

public static <T> void sort(List<T> list, Comparator<? super T> c)

第一个解决方案是最简单的解决方案,但如果您需要根据多个条件对GetTraders对象进行排序,那么第二个解决方案是最佳选择.

正如@Vaseph所指出的,如果你使用的是Java 8,生活会变得更加容易,因为你需要做的就是:

traders.sort((GetTraders trade1, GetTraders trade2) -> {
    return trade1.getBusinessName().compareTo(trade2.getBusinessName());
});

但是如果您遇到Comparable和Comparator接口的麻烦,我建议您先进入Java-8之前的解决方案,然后再进入功能接口的神奇世界.

为了完整起见,请在下面找到每个解决方案的示例:

1)基于可比的解决方案:

import java.util.ArrayList;
import java.util.Collections;
import java.util.List;

public class GetTraders1 implements Comparable<GetTraders1> {

    private String getTraderLegalName;
    private String businessName;
    private Object status;

    public GetTraders1(String getTraderLegalName, String businessName, String status) {
        this.getTraderLegalName=getTraderLegalName;
        this.businessName=businessName;
        this.status=status;
    }

    @Override
    public int compareTo(GetTraders1 that) {
        return this.getTraderLegalName.compareTo(that.getTraderLegalName);
    }

    @Override
    public String toString() {
        return "GetTraders [getTraderLegalName=" + getTraderLegalName + ", businessName=" + businessName + ", status=" + status + "]";
    }

    public static void main(String[] args) {

        GetTraders1 getTraders1 = new GetTraders1("1", "bn", "status");
        GetTraders1 getTraders2 = new GetTraders1("2", "bn", "status");
        GetTraders1 getTraders3 = new GetTraders1("3", "bn", "status");

        List<GetTraders1> list = new ArrayList<>();
        list.add(getTraders3);
        list.add(getTraders2);
        list.add(getTraders1);

        System.out.println(list);

        Collections.sort(list);

        System.out.println(list);

    }

}

2)基于比较器的解决方案

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

public class GetTraders2 {

    private String getTraderLegalName;
    private String businessName;
    private Object status;

    public GetTraders2(String getTraderLegalName, String businessName, String status) {
        this.getTraderLegalName=getTraderLegalName;
        this.businessName=businessName;
        this.status=status;
    }

    @Override
    public String toString() {
        return "GetTraders [getTraderLegalName=" + getTraderLegalName + ", businessName=" + businessName + ", status=" + status + "]";
    }

    public static void main(String[] args) {

        GetTraders2 getTraders1 = new GetTraders2("1", "bn", "status");
        GetTraders2 getTraders2 = new GetTraders2("2", "bn", "status");
        GetTraders2 getTraders3 = new GetTraders2("3", "bn", "status");

        List<GetTraders2> list = new ArrayList<>();
        list.add(getTraders3);
        list.add(getTraders2);
        list.add(getTraders1);

        System.out.println(list);

        Collections.sort(list, new Comparator<GetTraders2>() {

            @Override
            public int compare(GetTraders2 o1, GetTraders2 o2) {
                return o1.getTraderLegalName.compareTo(o2.getTraderLegalName);
            }

        });

        System.out.println(list);

    }

}