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;
}

Answer 1

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;
}

Answer 2

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);
}

Answer 3

我不明白你为什么要改变这段代码，但假设你已经把它测量为性能瓶颈，要么缓存createLocales的结果（全局或每个Thread使用一个懒惰地构建它的ThreadLocal）或者可能不是返回一个list，将langCode中的映射返回到懒惰实例化的值并缓存所需的SelectItem实例。