Method for String Building in java

Question

I have written a custom method to use StringBuilder in java. My Requirement is to create a method which accepts any number of arguments of any type and return String by concatenating the arguments.

eg. msgBuilder("Hello ",0," how"," are"," you ",2.5) return "Hello 0 how are you 2.5"

Here is my java code. Please Someone review my code and suggest If I did anything is wrong or Can I use this further in my projects.

 public class Test {
 public static void main(String[] args ){
 String msg = msgBuilder("Hello ",5," How ","are ","you");
 System.out.println(msg);
 }
 private static String msgBuilder(Object... params){
 StringBuilder sb = new StringBuilder();
 for(Object obj:params){
 sb.append(obj);
 }
 return sb.toString();
 }
 }

• h.j.k.: Any particular reason why you are reinventing-the-wheel?
• h.j.k.: Some logging frameworks allow parameterized String formatting, have you checked if your logging framework of choice has it? Also, are you on Java 8?
• stux_kill: Yes I am using java 8 and using apache4j Logger

Answer 1

I had this in mind:

private static String msgBuilder(Object... params) {
 StringBuilder sb = new StringBuilder();
 if (params.length > 0) {
 sb.append(params[0]);
 }
 for (int i = 1; i < params.length; ++i) {
 sb.append(" ").append(params[i]);
 }
 return sb.toString();
}

The above version allows you not to hardcode the white space delimiting your tokens. Instead of saying

String msg = msgBuilder("Hello ", 5, " How ", "are ", "you");

you can say succintly

String msg = msgBuilder("Hello", 5, "How", "are", "you");

Hope that helps.

Answer 2

Your approach

As pointed out by the other answers, you are practically hard-coding whitespaces in your arguments, which can get non-standard easily, even in your example. Otherwise, the use of StringBuilder is sound, although it wouldn't deal nicely with a single null value - the for-each loop will fail as it implicitly tries to get an Iterator for it.

Java 8

An alternative is to rely on the stream-based processing that Java 8 offers:

private static String format(Object... values) {
 if (values == null) {
 return "";
 }
 return Arrays.stream(values)
 .map(Objects::toString)
 .collect(Collectors.joining(" "));
}

1. Construct a Stream<Object> from values using Arrays.stream(T...).
2. map() each value using Objects.toString(Object) as a method reference.
3. collect() the stream into a String by joining(" ") them together.

• stux_kill: Will it be as efficient as StringBuilder()
• h.j.k.: Yes, it uses the new StringJoiner class as the underlying implementation, which in turn uses a StringBuilder.

Answer 3

I just decompiled the below code in java version "1.8.0_73" and found that compiler is automatically optimizing the code for strings

 String hello = "a" + "b" + "c" + " hello " + " world ";
 System.out.println("Hello World!!");
 String a="a";
 String b="b";
 String c="c";
 String d=a+b+c;
 System.out.println(d); 
 System.out.println(a +" yo "+ b); 

Code after decompiling

 String s = "abc hello world ";
 System.out.println("Hello World!!");
 String s1 = "a";
 String s2 = "b";
 String s3 = "c";
 String s4 = (new StringBuilder()).append(s1).append(s2).append(s3).toString();
 System.out.println(s4);
 System.out.println((new StringBuilder()).append(s1).append(" yo ").append(s2).toString());

• mdfst13: Hi. Welcome to Code Review! This may be insightful, but how does it relate to the question? I.e. what changes in the posted code would you make?
• munish: As per my understanding, the query asked was to create strings in an optimize way. e.g. while printing logs we append too many strings using +. So above method was appending the strings using StringBuilder() But when I decompiled the code the java compiler was doing this optimzation itself.

Answer 4

@coderodde has a good point about eliminating the need for white space.

I'd simply do it this way:

private static String buildString(Object... values) {
 if (values.length == 0) {
 return "";
 }
 StringBuilder result = new StringBuilder();
 for (Object value : values) {
 result.append(' ').append(value);
 }
 return result.substring(1);
}

• stux_kill: Nice Suggestion. Thanx!