为什么我的HashMap.get即使在输入正确的键和值后也返回空值？ [英] Why does my HashMap.get returns null value even after putting proper key,value?

问题描述

我试图从哈希映射中检索一些值，然后返回值，我检查密钥是否存在于映射中，并且此检查总是失败，从而导致null值。我已经重写了hash Code和equals方法。有人可以告诉我我在做什么错吗？

类字段：

  private static final List< String> DZ = new ArrayList< String>（）; 
 private static final Map< Participant，List< String>> subDz = new HashMap< Participant，List< String>>（）; 
  

我正在放入地图的方法：

  public static synchronized void handleSubs（String [] subData，String dz）{
 int [] lowdims = new int [subData.length]; 
 int [] highdims = new int [subData.length]; 
尝试{
 for（int i = 1; i< subData.length; i ++）{
 if（！subData [i] .equals（）&&！subData [ i）.equals（\ n））{
 if（i％2 == 0）{
 highdims [i] = Integer.parseInt（subData [i] .trim（））; 
} 
 else {
 lowdims [i] = Integer.parseInt（subData [i] .trim（））; $！
 
 
 $ b if（！DZ.isEmpty（））{
 DZ.clear（）; 
} 
 DZ.add（dz）; 
 allSubDZs.add（dz）; 
 int [] newlow = removeZeroes（lowdims）; 
 int [] newhigh = removeZeroes（highdims）; 
 allSubs.add（new Participant（newlow，newhigh））; 
 subDz.put（new Participant（newlow，newhigh），DZ）; 
} 
  

检索值的方法：

  public static List< String> getSubDz（Participant sub）{
 if（subDz.containsKey（sub））{
 return subDz.get（sub）; 
} 
 else {
 logger.info（订阅DZ不可用）; 
返回null; 
 
 
 
 
 
 
 $ getSubDz中的if检查总是失败，我把钥匙放在里面。  
 
 
 hashCode和equals方法： 
 
 
  @Override 
 public int hashCode（）{
 final int prime = 31; 
 int result = 1; 
 result = prime * result +（（DZ == null）？0：DZ.hashCode（））; 
返回结果; 
} 
 @Override 
 public boolean equals（final Object obj）{
 if（this == obj）{
 return true; 
} 
 if（obj == null）{
 return false; 
 
 if（this.getClass（）！= obj.getClass（））{
 return false; 
} 
 final SubscriptionHandler other =（SubscriptionHandler）obj; 
 if（DZ == null）{
 if（other.DZ！= null）{
 return false; 
} 
} else if（！DZ.equals（other.DZ））{
 return false; 
} 
返回true; 
  
 
 
解决方案
在密钥类上需要equals和hashcode。这将是您的案例中的参与者类。
 
I am trying to retrieve some values from a Hash Map, before returning the value I am checking if the key is present in the map or not, and this check always fails which results in null value. I have overridden hash Code and equals method as well. Could someone tell me what I am doing wrong here?

class fields:
 private static final List<String> DZ=new ArrayList<String>();
 private static final Map<Participant,List<String>> subDz=new HashMap<Participant,List<String>>();
Method where I am putting into the map:
    public static synchronized void handleSubs(String[] subData,String    dz){
    int[] lowdims=new int[subData.length];
    int[] highdims=new int[subData.length];
    try {
        for (int i=1;i<subData.length;i++){
            if (!subData[i].equals("") && !subData[i].equals("\n")){
                if (i%2==0){
                    highdims[i]=Integer.parseInt(subData[i].trim());
                }
                else {
                    lowdims[i]=Integer.parseInt(subData[i].trim());
                }
            }
        }
        if (!DZ.isEmpty()){
            DZ.clear();
        }
        DZ.add(dz);
        allSubDZs.add(dz);
        int[] newlow=removeZeroes(lowdims);
        int[] newhigh=removeZeroes(highdims);
        allSubs.add(new Participant(newlow,newhigh));
        subDz.put(new Participant(newlow,newhigh),DZ );
    }
Method where I am retrieving the values:
   public static List<String> getSubDz(Participant sub){
    if (subDz.containsKey(sub)){
        return subDz.get(sub);
    }
    else{
        logger.info("Subscription DZ not available");
        return null;
    }
}
The if check in the getSubDz always fails, even though I put the key in it. 

hashCode and equals methods:
   @Override
   public int hashCode() {
    final int prime = 31;
    int result = 1;
    result = prime * result + ((DZ == null) ? 0 : DZ.hashCode());
    return result;
}
   @Override
   public boolean equals(final Object obj) {
    if (this == obj) {
        return true;
    }
    if (obj == null) {
        return false;
    }
    if (this.getClass() != obj.getClass()) {
        return false;
    }
    final SubscriptionHandler other=(SubscriptionHandler)obj;
    if (DZ == null) {
        if (other.DZ != null) {
            return false;
        }
    } else if (!DZ.equals(other.DZ)) {
        return false;
    }
    return true;

解决方案
You need equals and hashcode on the key class. This would be the class Participant in your case.

                        
这篇关于为什么我的HashMap.get即使在输入正确的键和值后也返回空值？的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！