Can I use String[] as HashMap values in Java?

Question

I am a beginner in Java programming. I want to create a HashMap whose values are String[]'s.

Suppose I have a JTable parametersTable with values in columns 2, 3, and 4 that I wish to fetch from each row. Each three-value set constitutes a HashMap value (String[]).

HashMap<String, String[]> map = new HashMap<String, String[]>();
String[] row = {"one", "two", "three", "four", "five", "six", "seven","eight","nine","ten","eleven"};
for (int i=0; i<row.length; i++) {
map.put(row[i], new String[] {
   (String) parametersTable.getValueAt(i, 2),
   (String) parametersTable.getValueAt(i, 3),
   (String) parametersTable.getValueAt(i, 4)});
}
System.out.println(map);

The above code outputs:

{nine=[Ljava.lang.String;@187930f1, six=[Ljava.lang.String;@2a8000ab, four=[Ljava.lang.String;@4436b0fd, one=[Ljava.lang.String;@134bc965, seven=[Ljava.lang.String;@42e49d45, eleven=[Ljava.lang.String;@68cb58ea, ten=[Ljava.lang.String;@198bbc56, two=[Ljava.lang.String;@54464ee3, three=[Ljava.lang.String;@32aeff9b, five=[Ljava.lang.String;@90ed2c, eight=[Ljava.lang.String;@443d9864}

Why is the output something cryptic and not the values like I expect?

You might also consider the use of a guava Multimap. docs.guava-libraries.googlecode.com/git-history/v17.0/javadoc/… — Brett Okken
– Brett Okken, Commented Jul 31, 2014 at 1:58
I would consider using a List<String> instead, but that's just me — MadProgrammer
– MadProgrammer, Commented Jul 31, 2014 at 2:12
Your problem is, that .toString() on String[] does not print what you want. But the storing and retrieving works. Yo ucan use java.util.Arrays.toString(String[]). BTW: it is not so cryptic, it will print [ for Array, then the type (I is integer and objects print the type as Lpackage.Class;. In your case String) and then the system hashcode of the array object after the @. — eckes
– eckes, Commented Jul 31, 2014 at 22:55

eckes · Accepted Answer · 2014-07-31 23:02:07Z

2

Why is the output something cryptic and not the values like I expect?

[Ljava.lang.String;@ is the default representation of String arrays toString() method.

Use Arrays.toString method instead.

So instead of System.out.println(map) use this to get a meaningful representation

 for(Map.Entry<String, String[]> entry : map.entrySet()) {
       System.out.println(entry.getKey() + " -> " + Arrays.toString(entry.getValue()));
 }

edited Jul 31, 2014 at 23:02

eckes

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answered Jul 31, 2014 at 22:54

Ajay George

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Comments

slavik · Accepted Answer · 2014-07-31 22:51:55Z

1

Try this method :)

     static void print(HashMap<String, String[]> map) {

        StringBuilder builder = new StringBuilder();
        for(Map.Entry<String, String[]> e : map.entrySet()) {

            builder.append(e.getKey()).append(" -> [");
            boolean tmp = false;
            for(String s : e.getValue()) {
                if(tmp) {
                    builder.append(" ");
                }
                tmp = true;
                builder.append(s);

            }
            builder.append("]\n");

        }
        System.out.println(builder.toString());

    }

You got [Ljava.lang.String;@90ed2c because default method toString() for array was invoked.

answered Jul 31, 2014 at 22:51

slavik

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