Java Extracts Substrings

In Java, the java.lang.String class provides methods to extract substrings from a given string. In this tutorial, we will learn how to use the substring() method to extract substrings in Java.

Using the substring(int beginIndex) method:

The substring(int beginIndex) method takes an integer beginIndex as a parameter and returns a substring that starts from the specified index and goes until the end of the original string. The indexing is zero-based.

Example:

public class Main {
    public static void main(String[] args) {
        String str = "Hello, World!";
        String subStr = str.substring(7);
        System.out.println("Extracted substring: " + subStr);
    }
}

Output:

Extracted substring: World!

Using the substring(int beginIndex, int endIndex) method:

The substring(int beginIndex, int endIndex) method takes two integer parameters, beginIndex and endIndex. It returns a substring that starts from the specified beginIndex and goes up to, but not including, the specified endIndex. The indexing is zero-based.

Example:

public class Main {
    public static void main(String[] args) {
        String str = "Hello, World!";
        String subStr = str.substring(0, 5);
        System.out.println("Extracted substring: " + subStr);
    }
}

Output:

Extracted substring: Hello

Extracting substrings using string manipulation methods:

In some cases, you might need to extract a substring based on specific conditions or patterns. You can use various string manipulation methods, such as indexOf(), lastIndexOf(), or split(), in combination with the substring() method to achieve this.

Example:

public class Main {
    public static void main(String[] args) {
        String str = "apple,banana,orange";
        int indexOfFirstComma = str.indexOf(',');
        String firstFruit = str.substring(0, indexOfFirstComma);

        int indexOfLastComma = str.lastIndexOf(',');
        String lastFruit = str.substring(indexOfLastComma + 1);

        System.out.println("First fruit: " + firstFruit);
        System.out.println("Last fruit: " + lastFruit);
    }
}

Output:

First fruit: apple
Last fruit: orange

In conclusion, the substring() method in Java allows you to extract substrings from a given string. You can use this method in combination with other string manipulation methods to extract substrings based on specific conditions or patterns.

Extracting substrings from a string in Java: Extracting substrings involves obtaining a portion of a string, either based on indices or specific patterns.
Substring methods in Java: Java provides various substring methods in the String class to extract portions of a string.
Using substring() method in Java: The substring() method is a commonly used method to extract a substring from a string.
```
String str = "Hello, Java!";
String substring = str.substring(7); // Extracts substring from index 7 to the end
```
Java substring index and length: The substring(int beginIndex, int endIndex) method allows specifying both the start and end indices for substring extraction.
```
String str = "Hello, Java!";
String substring = str.substring(7, 11); // Extracts substring from index 7 to 10
```
Substring vs substring in Java: substring() and substring(int beginIndex, int endIndex) serve different purposes. The former starts from the specified index to the end, while the latter specifies both start and end indices.
Extracting multiple substrings from a string: Multiple substrings can be extracted by using a combination of substring() calls or other methods.
```
String str = "Java is awesome!";
String substring1 = str.substring(0, 4); // Java
String substring2 = str.substring(7, 9); // is
```

Substring extraction with regular expressions in Java: Regular expressions can be used for more complex substring extraction based on patterns.

import java.util.regex.Matcher;
import java.util.regex.Pattern;

String str = "The price is $50";
Pattern pattern = Pattern.compile("\\$\\d+");
Matcher matcher = pattern.matcher(str);

while (matcher.find()) {
    String match = matcher.group();
    System.out.println("Found: " + match);
}

Getting a portion of a string in Java: The substring() method is ideal for getting a portion of a string based on indices.
```
String str = "Extract this portion";
String portion = str.substring(8, 13); // Gets "this"
```

Extracting substrings with StringTokenizer in Java: StringTokenizer can be used to extract substrings based on delimiters.

String str = "Java:Programming:Language";
StringTokenizer tokenizer = new StringTokenizer(str, ":");
while (tokenizer.hasMoreTokens()) {
    String token = tokenizer.nextToken();
    System.out.println("Token: " + token);
}

Substring extraction and memory efficiency in Java: Extracting substrings might lead to increased memory usage if large substrings or frequent extractions are involved.

Substring extraction from the end of a string in Java: Extracting substrings from the end involves using the length of the string to calculate the start index.

String str = "Extract from end";
int endIndex = str.length();
int startIndex = endIndex - 3;
String endSubstring = str.substring(startIndex, endIndex); // Gets "end"

Common mistakes when extracting substrings in Java: Mistakes include using incorrect indices, not considering the inclusive/exclusive nature of indices, and not handling cases where the specified indices are out of bounds.