在Android的情况下，来自commons的StringUtils类是不可用的，所以我使用了这个

android.text.TextUtils.join(CharSequence delimiter, Iterable tokens)

http://developer.android.com/reference/android/text/TextUtils.html

//Note: if you have access to Java5+, 
//use StringBuilder in preference to StringBuffer.  
//All that has to be replaced is the class name.  
//StringBuffer will work in Java 1.4, though.

appendWithDelimiter( StringBuffer buffer, String addition, 
    String delimiter ) {
    if ( buffer.length() == 0) {
        buffer.append(addition);
    } else {
        buffer.append(delimiter);
        buffer.append(addition);
    }
}


StringBuffer parameterBuffer = new StringBuffer();
if ( condition ) { 
    appendWithDelimiter(parameterBuffer, "elementName", "," );
}
if ( anotherCondition ) {
    appendWithDelimiter(parameterBuffer, "anotherElementName", "," );
}

//Finally, to return a string representation, call toString() when returning.
return parameterBuffer.toString(); 

为什么你不在Java中做你在ruby中做的同样的事情，那就是在你将所有的片段添加到数组后才创建分隔符分隔的字符串?

ArrayList<String> parms = new ArrayList<String>();
if (someCondition) parms.add("someString");
if (anotherCondition) parms.add("someOtherString");
// ...
String sep = ""; StringBuffer b = new StringBuffer();
for (String p: parms) {
    b.append(sep);
    b.append(p);
    sep = "yourDelimiter";
}

你可能想要在一个单独的帮助方法中移动for循环，并且使用StringBuilder而不是StringBuffer…

编辑:修正了追加的顺序。

我个人经常使用以下简单的解决方案进行日志记录:

List lst = Arrays.asList("ab", "bc", "cd");
String str = lst.toString().replaceAll("[\\[\\]]", "");

还有一个最小值(如果你只是为了连接字符串而不想将Apache Commons或Gauva包含到项目依赖项中)

/**
 *
 * @param delim : String that should be kept in between the parts
 * @param parts : parts that needs to be joined
 * @return  a String that's formed by joining the parts
 */
private static final String join(String delim, String... parts) {
    StringBuilder builder = new StringBuilder();
    for (int i = 0; i < parts.length - 1; i++) {
        builder.append(parts[i]).append(delim);
    }
    if(parts.length > 0){
        builder.append(parts[parts.length - 1]);
    }
    return builder.toString();
}

不要使用join, delimiter或StringJoiner方法和类 在Android N和O版本下不工作。否则使用简单的代码逻辑 作为;

 List<String> tags= emp.getTags();
        String tagTxt="";
        for (String s : tags) {
            if (tagTxt.isEmpty()){
                tagTxt=s;
            }else
                tagTxt= tagTxt+", "+s;
        }