Avoid instantiating new objects inside loops in java

Question

I would like to avoid crating the new instance of SelectItem in side the loop. Could you please help me how can i avoid it.

public List<SelectItem> createLocales() {
    final List<SelectItem> enabledLocales = new ArrayList<SelectItem>();
    final List<String> langCodes = labeldbservice.getEnabledLocales();
    LOGGER.debug("getEnabledLocales: size={0}", langCodes);
    for (final String langCode : langCodes) {
        enabledLocales.add(new SelectItem(langCode, LocaleUtils.toLocale(langCode).getDisplayName()));
    }
    return enabledLocales;
}

Why would you like to avoid it? This seems to be the cleanest way to add a `SelectItem` to `enabledLocales` for each `langCode`. — jlordo, Jul 25 '13 at 09:29
Then how would u create different objects for different langCode? — Juned Ahsan, Jul 25 '13 at 09:30
possible duplicate of [PMD: Avoid instantiating new objects inside loops](http://stackoverflow.com/questions/17340421/pmd-avoid-instantiating-new-objects-inside-loops) — Andrew Janke, Mar 16 '14 at 04:58

score 1 · Answer 1 · edited Jan 14 '14 at 13:35

public List<SelectItem> createLocales() {
    final List<SelectItem> enabledLocales = new ArrayList<SelectItem>();
    final List<String> langCodes = labeldbservice.getEnabledLocales();
    final SelectItem sItem = new SelectItem();

    LOGGER.debug("getEnabledLocales: size={0}", langCodes);
    for (final String langCode : langCodes) {
        sItem.setValue(langCode);
        sItem.setLabel(LocaleUtils.toLocale(langCode).getDisplayName());
        enabledLocales.add(sItem);
    }
    return enabledLocales;
}

score 1 · Answer 2 · answered Mar 16 '14 at 04:48

I solved this PMD Issue by creating a method which will return a new object. I will call this method in loop to get new object.
For your code it would be something like this.

public List<SelectItem> createLocales() {
    final List<SelectItem> enabledLocales = new ArrayList<SelectItem>();
    final List<String> langCodes = labeldbservice.getEnabledLocales();
    LOGGER.debug("getEnabledLocales: size={0}", langCodes);
    for (final String langCode : langCodes) {
        enabledLocales.add(getNewSelectItem(langCode, LocaleUtils.toLocale(langCode).getDisplayName()));
    }
    return enabledLocales;
}

public SelectItem getNewSelectItem(String langCode, String displayName) {
    return new SelectItem(langCode, displayName);
}

score 0 · Answer 3 · answered Jul 25 '13 at 09:35

0

I do not see why you want to change this code but assuming that you have measured this to be a performance bottleneck, either cache the result of createLocales (globally or per Thread using a ThreadLocal that lazily builds it up) or perhaps instead of returning a list, return a map from langCode to values that lazily instantiate and cache the required SelectItem instances.

answered Jul 25 '13 at 09:35

boggle

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initially i had used map only but for retrieval operation at UI side is slow with ma so i am trying to using list interface – Vijay Kumar Jul 25 '13 at 10:36

Avoid instantiating new objects inside loops in java

3 Answers3