Java Cookbook

Putting Strings Together with + and StringBuffer

Problem

You need to put some String pieces back together.

Solution

Use string concatenation: the + operator. The compiler will construct a StringBuffer for you and use its append( ) methods. Or better yet, construct it yourself. Conveniently, the append( ) method returns a reference to the StringBuffer itself, so that statements like the .append(...).append(...) are fairly common. You might even see this third way in a toString( ) method. Example 3-2 shows the three ways of concatenating strings.

Example 3-2. StringBufferDemo.java

/**
 * StringBufferDemo: construct the same String three different ways.
 */
public class StringBufferDemo {
    public static void main(String[] argv) {
        String s1 = "Hello" + ", " + "World";
        System.out.println(s1);

        // Build a StringBuffer, and append some things to it.
        StringBuffer sb2 = new StringBuffer(  );
        sb2.append("Hello");
        sb2.append(',');
        sb2.append(' ');
        sb2.append("World");

        // Get the StringBuffer's value as a String, and print it.
        String s2 = sb2.toString(  );
        System.out.println(s2);

        // Now do the above all over again, but in a more 
        // concise (and typical "real-world" Java) fashion.

        StringBuffer sb3 = new StringBuffer(  ).append("Hello").
            append(',').append(' ').append("World");
        System.out.println(sb3.toString(  ));

        // Exercise for the reader: do it all again but without
        // creating ANY temporary variables.
    }
}

In fact, all the methods that modify more than one character of a StringBuffer’s contents ...