Java Cookbook

Aligning Strings

Problem

You want to align strings left, right, or centered.

Solution

Do the math yourself, and use substring (Section 3.2) and a StringBuffer (Section 3.4). Or, just use my StringAlign class, which is based on the java.text.Format class.

Discussion

Centering, or left- or right-aligning text, comes up surprisingly often. Suppose you want to print a simple report with centered page numbers. There doesn’t seem to be anything in the standard API that will do the job fully for you. But I have written a class called StringAlign that will. Here’s how you might use it:

/* Align a page number on a 70-character line. */
public class StringAlignSimple {

    public static void main(String[] args) {
        // Construct a "formatter" to center strings.
        StringAlign formatter = new StringAlign(70, StringAlign.JUST_CENTER);
        // Try it out, for page "i"
        System.out.println(formatter.format("- i -"));
        // Try it out, for page 4. Since this formatter is
        // optimized for Strings, not specifically for page numbers,
        // we have to convert the number to a String
        System.out.println(formatter.format(Integer.toString(4)));
    }
}

If we compile and run this class, it prints the two demonstration line numbers centered, as shown:

> jikes +E -d . StringAlignSimple.java
> java StringAlignSimple
                                - i -
                                  4
>

Here is the code for the StringAlign class. Note that this class extends a class called Format . In the package java.text there is a series of Format classes; they all have at least one method called format( )