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Prefer String Offset-Based Methods for Finding Substrings

Medium
performanceefficiency

What is it?​

This practice highlights the importance of using offset-based methods for finding substrings in String objects, instead of repeatedly creating new String instances using the substring method.

Why apply it?​

Using the substring method in combination with other String methods like indexOf or lastIndexOf can lead to unnecessary creation of new String instances. This can cause performance issues, especially in loops or when working with large strings.

How to fix it?​

Opt for offset-based methods that take start position parameters directly, which help avoid the creation of additional String instances.

Examples​

Example 1:​

Negative​

This example uses substring followed by indexOf, resulting in unnecessary creation of a new String.

public class SubstringExample {
    public static void main(String[] args) {
        String text = "Hello, welcome to the world of Java!";
        int start = 7;
        int index = text.substring(start).indexOf("welcome");
        
        if (index != -1) {
            System.out.println("Found 'welcome' at index: " + (index + start));
        }
    }
}

Example 2:​

Positive​

This example uses the offset-based indexOf method to find a substring starting from a specified index without creating a new String.

public class OffsetExample {
    public static void main(String[] args) {
        String text = "Hello, welcome to the world of Java!";
        int start = 7;
        int index = text.indexOf("welcome", start);
        
        if (index != -1) {
            System.out.println("Found 'welcome' at index: " + index);
        }
    }
}

Negative​

This example wrongly creates a new String with substring before using lastIndexOf, leading to inefficiency.

public class SubstringLastIndexExample {
    public static void main(String[] args) {
        String text = "The quick brown fox jumps over the lazy dog. quick!";
        int start = 4;
        int index = text.substring(0, start).lastIndexOf("quick");
        
        if (index != -1) {
            System.out.println("Found 'quick' at index: " + index);
        }
    }
}

Example 3:​

Positive​

Here, the offset-based lastIndexOf method is used to efficiently find a substring without creating extra String objects.

public class OffsetLastIndexExample {
    public static void main(String[] args) {
        String text = "The quick brown fox jumps over the lazy dog. quick!";
        int start = 4;
        int index = text.lastIndexOf("quick", start);
        
        if (index != -1) {
            System.out.println("Found 'quick' at index: " + index);
        }
    }
}