how to access to end element of a map?

Question

I have this method:

    public String nodePropertyGenerator(Map<String,Object> properties){
    String prop="";
    for(Map.Entry<String, Object> entry : properties.entrySet()) {
        prop += entry.getKey() + ":'" +entry.getValue()+"' ,";
        Iterator iterator = properties.entrySet().iterator(); 
    }
    return prop;
}

I want to this method return a string like this:

name:'hossein' , age:'24' , address:'khorram'

so I want to check if my map's element be end element , it remove "," from end of string. how to do that. please help me. thanks

[Refer this one, this might solve your problem][1] [1]: http://stackoverflow.com/questions/3527216/accessing-the-last-entry-in-a-map — global, Jul 14 '14 at 12:30

score 4 · Accepted Answer · answered Jul 14 '14 at 12:07

One way is to add a boolean variable, set it to true before entering the loop, and use it to decide if you need a comma before adding the next component, like this:

boolean isFirst = true;
StringBuilder res = new StringBuilder();
for (Map.Entry<String, Object> entry : properties.entrySet()) {
    if (!isFirst) {
        res.append(", ");
    }
    isFirst = false;
    res.append(entry.getKey());
    res.append(":'");
    res.append(entry.getValue());
    res.append("'");
}

Note that using the concatenation operator on immutable strings in a loop is inefficient. You should use StringBuilder instead.

it worked . thanks my friend. I'm happy for your help.good luck — user3807246, Jul 14 '14 at 12:23

Jon Skeet · Answer 2 · 2014-07-14T12:14:09.943

2

You can't tell whether the current iteration is the last one. I suggest you use a StringBuilder instead of repeated string concatenation, then just trim the length at the end:

StringBuilder builder = new StringBuilder();
for (Map.Entry<String, Object> entry : properties.entrySet()) {
    builder.append(entry.getKey())
           .append(":'")
           .append(entry.getValue())
           .append("' ,");
}
if (builder.length() > 0) {
    builder.setLength(builder.length() - 2);
}
return builder.toString();

edited Jul 14 '14 at 12:14

answered Jul 14 '14 at 12:07

Jon Skeet

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A touch faster. :) +1 – Keppil Jul 14 '14 at 12:08
Shouldn't that be `builder.length() - 2`? – tobias_k Jul 14 '14 at 12:14
@tobias_k: Whoops, yes, sorry. Fixed. – Jon Skeet Jul 14 '14 at 12:14

fabian · Answer 3 · 2014-07-14T12:30:21.767

Java 8 has a class to do this: java.util.StringJoiner

You would use it like this:

StringJoiner stringJoiner = new StringJoiner("' ,");
for(Map.Entry<String, Object> entry : properties.entrySet()) {
    stringJoiner.add(entry.getKey() + ":'" +entry.getValue());
}
return stringJoiner.toString();

Or alternatively you could use a Stream to do this:

return properties.entrySet().stream()
                 .map(entry -> entry.getKey() + ":'" +entry.getValue())
                 .collect(Collectors.joining("' ,"));

how to access to end element of a map?

3 Answers3