在多個獨立的hashMap對象中搜索特定鍵

Question

在我開始編程我的解決方案之前，我有一個稍微理論化的問題，我想要澄清......

背景。 我需要在2個（或更多）MS Access文件之間進行比較。

每個文件都應包含在其他文件中找到的數據。

由於我遇到JDBC的“限制”並連接到Access結果集（它們只能向前滾動！）我創建了“java對象”（類）來模擬結果集的結構。

本質上我有一個對象來模擬結果集中的單個記錄行（讓我們稱之為rowSet）然后resSet對象有一個rowSets的“數組”。

但是為了“加快速度”，我會捕獲鍵和索引列中的值，並為相關的rowSet對象創建一個'key_Index'的hashMap。

我比較然后做以下。

取第一個resSet對象（用作主服務器），從中收集個人Key_Index的hashmaps（讓我們稱之為'aKey'......

現在使用這個'aKey'對象搜索其他可用的resSet對象，看看是否有任何包含與'aKey'中的值匹配的key_Index的值。

然而，我剛剛有一個相當討厭的想法。

如果我在其他一個resSet對象上使用代碼resSet.get（aKey），我會遇到問題，因為'aKey'對象顯然不是同一個對象 - 盡管它的內容應該是相同的（即可比較）。

我不得不說，當我閱讀我的問題時，我認為它的措辭不夠......所以我想我會包含我創建的課程副本......

重要的部分：

members：challenge - “結果集”類型對象的arrayList。

方法：runChallenge（）

package KWhite;

/**
 * the RScomparator is designed for the instance of comparing a double entry database system, as
 * often occurs in localy run medical trials data.
 * 
 * The double entry is to ensure that there are no errors made during input, the entry is performed
 * in separate independant instances. The RScolmparator object is specifically able to take any
 * number of result sets as its input (ie queries from multiple independantly created databases)
 * 
 * It should be recognised that this object should probably be called as part of a DBcomparator
 * object.
 * 
 */
//imports here

//import of logger class and required dependencies...
import java.util.ArrayList;
import java.util.HashMap;

import org.apache.log4j.PropertyConfigurator;

import MrBlue.DB_Table;
import TawuaiLogger.tawuaiLogger;

public class RScomparator {

//Static variables

//the logger instance
private static final TawuaiLogger.tawuaiLogger errLog = new tawuaiLogger("RScomparator");

//class member variables

/** this is a selection of ResSet objects that are going to have thier data challenged */
private ArrayList<ResSet_KW> challenge;
/**the name of the current table being challenged*/
private String tableName;
/**a 'table' object for meta data reference purposes, this can be used for getting column types etc */
private DB_Table table;

//These are our report objects
/**a report array for challenge failures */
private ArrayList<report_KW> fail;
/**a report array for errors, ie no challenger able to be made, no equivalent value found */
private ArrayList<report_KW> errors;
/**a report array for the good values */
private ArrayList<report_KW> success;

/** this is either the main class or the constructor
 * 
 * If it is a constructor rename to reflect the name of the class
 * @param args
 */
public RScomparator(DB_Table t) //TODO add arguments as required
{
    PropertyConfigurator.configure("Log4j.properties");
    // TODO Auto-generated method stub
    challenge = new ArrayList<ResSet_KW>();
    //initialise our report objects for this challenge scenario
    fail =  new ArrayList<report_KW>();
    errors = new ArrayList<report_KW>();
    success = new ArrayList<report_KW>();
    table = t;
    tableName = t.getTblName();
}

//class methods go here

/**
 * add a result set object into this comparator
 * 
 * @param r the result set object being inserted into this challenge.
 * 
 */
public void addChallenger(ResSet_KW r)
{
this.challenge.add(r);  
}


/**
 * this runs the comparison process...
 * Although no details in of itself are returned it calls other methods that do return a value
 *
 */

public void runChallenge()
{
//TODO finish this method, creating a report object on the way

    //these are the 2 result set objects that will be compared
    ResSet_KW gold = new ResSet_KW  ();
    ResSet_KW silver = new ResSet_KW ();



    //ensure the challenger list has objects in it.
    if(challenge.size() < 2)
    {
        //it must have 2 objects..
        errLog.add(3, "there are no results available for comparison of table " + this.tableName);
        //either way we should create report object.
        this.errors.add( new report_KW(tableName));
        //break out of the method.
        return;
    }

    //get the first row of data

    gold = challenge.get(0);//the first result set.

    //for each column in the result set, perform a search for the same key in the others..
    for(HashMap<String, String> c : gold.getRS().keySet())
    {//c is the key value in the map
        //cycle over the challenge object
        for (int i=1; i<challenge.size(); i++)//we don't want to use the first element, so start from 1 not zero
        {
            silver = challenge.get(i);
            if (silver.hasKey(c))
            {
                //a temp object for meta data referencing

                //only get the actual result values if there is a match
                Column_KW a = gold.getRS().get(c);
                Column_KW b = silver.getRS().get(c);
                //make the comparison
                a.compareTo(b, this.table);
                //get the reports from the comparison
                for(report_KW k :a.getFailure())
                    {
                    this.fail.add(k);
                    }
                for(report_KW k :a.getPassed())
                {
                    this.success.add(k);
                }
                for(report_KW k :a.getPassed())
                {
                this.errors.add(k);
                }
            }
            else
            {
                break;//return to the next item in the for loop
            }
        }
    }









}


/**
 *a helper method to create the error message creator
 *@ param m the extra message if any, 
 *@return s the full message
 */
private String getErrMessage(String m) {
    //the third element in the current stact trace should be the calling method
    StackTraceElement caller = Thread.currentThread().getStackTrace()[3];
    String s = m + "\ncalled from line " + caller.getLineNumber()
            + "\nmethod: " + this.getClass() + "." + caller.getMethodName();
        return s;
    }
}//end class

PS。 我的代碼或更多歡迎的任何coments

提前致謝

大衛

編輯：我剛剛發現這個問題， 嵌套映射或java中的組合鍵這將是我的解決方案，創建一個'自定義'key_Index對象，然后為它定義一個hashcode（）和equals對象。 但是我已經為我的key_index對象使用了'hashMap'，所以這是否會在我注意到的地方自動執行？

Answer 1

你說 ：

如果我在其他一個resSet對象上使用代碼resSet.get（aKey），我會遇到問題，因為'aKey'對象顯然不是同一個對象 - 盡管它的內容應該是相同的 （即可比較）。

您必須分別實現equals()和hashcode() 。 實現equals()是不夠的，如果對象相等， hashcode()必須相同。

例：

import java.util.HashMap;
import java.util.Map;

class A {
    String name;
    Integer number;

    public A(String name, Integer number) {
    super();
    this.name = name;
    this.number = number;
    }

}

class B {
    String name;
    Integer number;

    public B(String name, Integer number) {
    super();
    this.name = name;
    this.number = number;
    }

    @Override
    public boolean equals(Object obj) {
    if (obj instanceof B) {
        return obj == this || (name.equals(((B) obj).name) && number.equals(((B) obj).number));
    }
    return false;
    }

    @Override
    public int hashCode() {
    return name.hashCode() + number.hashCode();
    }
}

public class TestHashMap {

    public static void main(String... args) {
        A a1 = new A("a", 1);
        A anotherA1 = new A("a", 1);

        Map<A, String> as = new HashMap<A, String>();

        as.put(a1, "a1");

        System.out.println(as.get(anotherA1)); // prints null

        B b1 = new B("b", 1);
        B anotherB1 = new B("b", 1);

        Map<B, String> bs = new HashMap<B, String>();

        bs.put(b1, "b1");

        System.out.println(bs.get(anotherB1)); // prints b1

    }

}