如何在java中将对象添加到ArrayList中

Question

这里有两个类,查询语句和stackov.arraylist用于存储查询句子类的对象.但是最近添加的对象覆盖了前一个对象.如何添加对象以使它们不被覆盖？

QuerySentence.java

public class QuerySentence {

    public static String query;
    public static String label;
    public QuerySentence(){

    }
    public QuerySentence(String query,String label){
        this.query = query;
        this.label = label;
    }
}  

Stackov.java

package QueryClassifier;

import java.util.ArrayList;

public class stackov {

    public static void main(String args[])
    {
        QuerySentence qs1 = new QuerySentence("What state produces the best lobster to eat","LOCATION");
        QuerySentence qs2 = new QuerySentence("What is Dick Clark's birthday","DATE");
        ArrayList<Object> doclist = new ArrayList<Object>();

            doclist.add(0,qs1);
            doclist.add(1,qs2);

            int size = doclist.size();
               while(size>0)
               {
                    QuerySentence qs3 = (QuerySentence) doclist.get(size-1);
                    System.out.println("\nin loop : " + qs3.label + qs3.query);
                    size--;
                }

    }
}   

Answer 1

问题不是来自你的循环,而是来自你的班级QuerySentence.您正在创建静态对象,这意味着您不会为类的不同实例创建不同的字段,但该类将只具有它们的唯一副本.那么这里发生了什么,你将这些价值分配给你的班级QuerySentence:

QuerySentence qs1 = new QuerySentence("What state produces the best lobster to eat","LOCATION");

然后用这个删除它:

QuerySentence qs2 = new QuerySentence("What is Dick Clark's birthday","DATE");

当你ArrayList在你的循环中添加两个对象时,你将打印两个结果.但只有qs2的结果.static从您的字段声明中删除它将正常工作:

public String query;
public String label;

添加时,您无需索引查询语句.

doclist.add(qs1);
doclist.add(qs2);

而且你也可以改善你的循环.你可以这样做:

ArrayList<QuerySentence> doclist = new ArrayList<QuerySentence>();

// some code...

for(QuerySentence q : doclist)
{
    System.out.println("In loop : " + q.label + q.query);
}

还请记住Java约定:您的类应以大写(Stackov)开头.如果你还对封装工作,这是更好地宣布你的领域private,创造getters和setters他们.有了这个你for-statement应该看起来像这样:

for(QuerySentence q : doclist)
{
    System.out.println("In loop : " + q.getLabel() + q.getQuery());
}