contains
method, indexOf
method, matches
method with regular expressions and Pattern
and Matcher
classes.Table of Contents
- Introduction
- Using
String.contains
Method - Using
String.indexOf
Method - Using
String.matches
Method with Regular Expressions - Using
Pattern
andMatcher
Classes - Conclusion
Introduction
Strings in Java are sequences of characters used to represent text. Checking if a string contains a specific substring can be done using various methods, each with its own advantages and use cases.
Using String.contains
Method
The contains
method checks if a string contains a specified sequence of characters.
Example
public class SubstringCheckExample {
public static void main(String[] args) {
String str = "Hello, world!";
String substr1 = "world";
String substr2 = "Java";
System.out.println(containsSubstring(str, substr1)); // true
System.out.println(containsSubstring(str, substr2)); // false
}
public static boolean containsSubstring(String str, String substr) {
return str.contains(substr);
}
}
Explanation
str.contains(substr)
: Returnstrue
ifstr
containssubstr
,false
otherwise.
Using String.indexOf
Method
The indexOf
method returns the index within the string of the first occurrence of the specified substring, or -1
if the substring is not found.
Example
public class SubstringCheckExample {
public static void main(String[] args) {
String str = "Hello, world!";
String substr1 = "world";
String substr2 = "Java";
System.out.println(containsSubstring(str, substr1)); // true
System.out.println(containsSubstring(str, substr2)); // false
}
public static boolean containsSubstring(String str, String substr) {
return str.indexOf(substr) != -1;
}
}
Explanation
str.indexOf(substr) != -1
: Returnstrue
ifstr
containssubstr
,false
otherwise.
Using String.matches
Method with Regular Expressions
The matches
method can be used with regular expressions to check if a string contains a substring. However, this method is generally used for full string matching rather than partial matching.
Example
public class SubstringCheckExample {
public static void main(String[] args) {
String str = "Hello, world!";
String substr1 = "world";
String substr2 = "Java";
System.out.println(containsSubstring(str, substr1)); // true
System.out.println(containsSubstring(str, substr2)); // false
}
public static boolean containsSubstring(String str, String substr) {
return str.matches(".*" + substr + ".*");
}
}
Explanation
str.matches(".*" + substr + ".*")
: Uses a regular expression to check ifstr
containssubstr
. The.*
before and after the substring allows for any characters to be present before or after the substring.
Using Pattern
and Matcher
Classes
The Pattern
and Matcher
classes from the java.util.regex
package provide more flexibility and control when working with regular expressions.
Example
import java.util.regex.Matcher;
import java.util.regex.Pattern;
public class SubstringCheckExample {
public static void main(String[] args) {
String str = "Hello, world!";
String substr1 = "world";
String substr2 = "Java";
System.out.println(containsSubstring(str, substr1)); // true
System.out.println(containsSubstring(str, substr2)); // false
}
public static boolean containsSubstring(String str, String substr) {
Pattern pattern = Pattern.compile(Pattern.quote(substr));
Matcher matcher = pattern.matcher(str);
return matcher.find();
}
}
Explanation
Pattern.compile(Pattern.quote(substr))
: Compiles the regular expression.Pattern.quote
is used to escape any special characters in the substring.matcher.find()
: Returnstrue
if the substring is found in the string,false
otherwise.
Conclusion
Checking if a string contains a substring in Java can be accomplished using various methods, including the contains
method, indexOf
method, matches
method with regular expressions, and the Pattern
and Matcher
classes. Each method has its own advantages and specific use cases:
- The
contains
method is straightforward and easy to use. - The
indexOf
method is useful if you also need the index of the substring. - The
matches
method with regular expressions provides a way to use regex for substring checks, though it's more commonly used for full string matching. - The
Pattern
andMatcher
classes provide a flexible and powerful way to work with regular expressions, especially for complex patterns.
By understanding these methods, you can choose the most appropriate one for your specific use case when working with strings in Java.
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