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String Class and Methods in Java

String Class and Methods in Java

The `String` class in Java is part of the `java.lang` package and is used to represent a sequence of characters. Strings in Java are immutable, meaning that once a `String` object is created, its value cannot be changed. The `String` class provides various methods to manipulate and perform operations on strings.


1. Creating Strings:

Strings can be created in Java using the following methods:

// Using string literal

String str1 = "Hello, World!";

// Using the new keyword

String str2 = new String("Hello, World!");


2. String Length:

The `length()` method returns the length of the string (number of characters).


String str = "Hello, World!";

int length = str.length(); // Returns 13


3. Concatenation:

The `concat()` method or the `+` operator is used for string concatenation.


String str1 = "Hello";

String str2 = "World";

String result = str1.concat(", ").concat(str2); // or, str1 + ", " + str2


4. Substring:

The `substring()` method is used to extract a portion of the string.

String str = "Hello, World!";

String subStr = str.substring(7); // Returns "World!"


5. String Comparison:


String comparison can be done using the `equals()` method for content comparison and `compareTo()` for lexicographical comparison.


String str1 = "Hello";

String str2 = "World";

boolean isEqual = str1.equals(str2); // Returns false

int result = str1.compareTo(str2); // Returns a negative value


6. Changing Case:

The `toUpperCase()` and `toLowerCase()` methods change the case of the string.

String str = "Hello, World!";

String upperCase = str.toUpperCase(); // Returns "HELLO, WORLD!"

String lowerCase = str.toLowerCase(); // Returns "hello, world!"


7. String Formatting:

The `format()` method is used to format strings similarly to `printf` in C.

String formattedStr = String.format("Value: %d, Text: %s", 42, "Java");


8. Checking Substring:

The `contains()` method checks if a string contains a specified sequence of characters.


String str = "Hello, World!";

boolean containsHello = str.contains("Hello"); // Returns true



9. Trimming Whitespace:

The `trim()` method removes leading and trailing whitespaces.


String str = "   Hello, World!   ";

String trimmedStr = str.trim(); // Returns "Hello, World!"


10. Converting to Other Types:

The `valueOf()` method is used to convert other data types to strings.


int number = 42;

String str = String.valueOf(number); // Converts int to String



These are some of the commonly used methods provided by the `String` class in Java. Understanding and using these methods effectively will enhance your ability to work with strings in Java.

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