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Java Java Data Structures Exploring the Java Collection Framework Maps

Posted by Viktor Kuryshev
Viktor Kuryshev
2,021 Points

System.out.printf("%s", hashTagCounts); How Map is converted into String?

It is not clear for me, why we did not need a loop to get every value from Map to print it, how printf converts Map Array into string. I assume the problem is that i can not trace it through documentation. I found method listed bellow. As i understans this method takes Map as object - but how can I trace how it treats it? Links to documentation traces would be mostly appreciated. Thank you.

printf(String format, Object... args) A convenience method to write a formatted string to this output stream using the >specified format string and arguments.

1 Answer

Alexander Nikiforov
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Alexander Nikiforov
Java Web Development Techdegree Graduate 22,175 Points
Alexander Nikiforov
.a{fill-rule:evenodd;}techdegree seal-36
Alexander Nikiforov
Java Web Development Techdegree Graduate 22,175 Points

public class HashMap<K,V> extends AbstractMap<K,V>

that is why you need to dig into AbstractMap

Online for example you can find it here:

http://grepcode.com/file/repository.grepcode.com/java/root/jdk/openjdk/6-b14/java/util/AbstractMap.java#AbstractMap.toString%28%29

The same thing with ArrayList or others, just go to the eldest parent possible and check code 

    /**
     * Returns a string representation of this map.  The string representation
     * consists of a list of key-value mappings in the order returned by the
     * map's <tt>entrySet</tt> view's iterator, enclosed in braces
     * (<tt>"{}"</tt>).  Adjacent mappings are separated by the characters
     * <tt>", "</tt> (comma and space).  Each key-value mapping is rendered as
     * the key followed by an equals sign (<tt>"="</tt>) followed by the
     * associated value.  Keys and values are converted to strings as by
     * {@link String#valueOf(Object)}.
     *
     * @return a string representation of this map
     */
    public String toString() {
        Iterator<Entry<K,V>> i = entrySet().iterator();
        if (! i.hasNext())
            return "{}";

        StringBuilder sb = new StringBuilder();
        sb.append('{');
        for (;;) {
            Entry<K,V> e = i.next();
            K key = e.getKey();
            V value = e.getValue();
            sb.append(key   == this ? "(this Map)" : key);
            sb.append('=');
            sb.append(value == this ? "(this Map)" : value);
            if (! i.hasNext())
                return sb.append('}').toString();
            sb.append(',').append(' ');
        }
    }