CODEWITHSUNDEEP
javahashmapkeyduplicates
hanbumpark
hanbumpark

Reputation: 233

Why does this hashmap have the same key twice?

// same X, Y value text.
    TextInfo currXY = new TextInfo( text );

    ArrayList<TextPosition> currTextArray = textComposition.get( currXY );
    if( currTextArray != null ){
        currTextArray.add( text ); 
    } else {
        ArrayList<TextPosition> newTextArray = new ArrayList<TextPosition>();
        newTextArray.add( text );
        if( textComposition.containsKey( currXY )){
            System.out.println( "processTextPosition : containsKEy ");
        }
        textComposition.put( currXY , newTextArray );
    }

A HashMap can't have duplicate or same key, right?

I get all entry from hashmap and put these entries into a new hashmap.

It proceed like same key. 

lineSortingMap = new HashMap< TextInfo, ArrayList<TextPosition> > ();     
    for ( Map.Entry< TextInfo, ArrayList<TextPosition> > entry : textComposition.entrySet() ) {
        TextInfo key = (TextInfo)entry.getKey();
        ArrayList<TextPosition> arrayTextPositions = entry.getValue();
        if( lineSortingMap.containsKey( key ) ){
            System.out.println("WTFcontainsKey : " + " " + key + " " + key.getX() + " " + key.getY() );
        }
        else{
            lineSortingMap.put( key , arrayTextPositions );
        }
    }

result: 

WTFcontainsKey :  analyzeSrc.TextInfo@4c5 75.307 603.85535

WTFcontainsKey :  analyzeSrc.TextInfo@4c5 71.74238 603.85535

WTFcontainsKey :  analyzeSrc.TextInfo@4c4 66.36187 612.82837

...

Can you explain what happens here?

Why doesn't it print "processTextPosition : containsKey"?

Upvotes: 1

Views: 1316

Answers (3)

Sean Patrick Floyd
Sean Patrick Floyd

Reputation: 299218

Probably because your Key Object doesn't override equals() and hashCode() correctly.

See the docs of Object.hashCode() and the Section Object as a Superclass from the Java Tutorial

Or even better: Read Effective Java (2nd Ed) by Joshua Bloch

Upvotes: 4

Bharat Sinha
Bharat Sinha

Reputation: 14373

For using a object which you have created as a key in Map you should overwrite hashCode() and equals() methods. I am pretty sure that your class TextInfo doesn't provide the implementation for the same.

Upvotes: 0

Joachim Sauer
Joachim Sauer

Reputation: 308269

It's hard to know without seeing the full code, but I'm reasonably sure that your TextInfo class does not correctly implement equals() and hashCode(). Having those two methods implemented is a prerequisite to being useful as a key in a HashMap.

Upvotes: 4

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