Java Cookbook

Taking Strings Apart with Substrings

Problem

You want to break a string apart into substrings by position.

Solution

Use the String object’s substring( ) method.

Discussion

The substring( ) method constructs a new String object made up from a run of characters contained somewhere in the original string, the one whose substring( ) you called. The name of this method, substring(), violates the stylistic dictum that words should be capitalized; if Java were 100.0% consistent, this would be named subString. But it’s not; it’s substring. The substring method is overloaded: both forms require a starting index. The one-argument form returns from startIndex to the end. The two-argument form takes an ending index (not a length, as in some languages), so that an index can be generated by the String methods indexOf( ) or lastIndexOf( ). Note that the end index is one beyond the last character!

// File SubStringDemo.java
public static void main(String[] av) {
    String a = "Java is great.";
    System.out.println(a);
    String b = a.substring(5);    // b is the String "is great."
    System.out.println(b);
    String c = a.substring(5,7);// c is the String "is"
    System.out.println(c);
    String d = a.substring(5,a.length(  ));// d is "is great."
    System.out.println(d);
}

This prints the following when run:

> java SubStringDemo
Java is great.
is great.
is
is great.
>