Strings

Introduction

A string in Java is a sequence of characters, used to store and manipulate text. In Java, strings are objects of the String class, which provides various methods to work with text data.

Why Use Strings?

Store Names and Messages – Example: Usernames, messages in chat applications.
File Handling – Read and write text files.
Data Processing – Extract and manipulate information from text.
Web Development – URLs, form inputs, and responses.

Creating Strings in Java

Strings can be created in multiple ways:

1. Using String Literals

String greeting = "Hello, World!";
System.out.println(greeting);

Java optimizes memory usage by storing string literals in a string pool.

2. Using the `new` Keyword

String message = new String("Hello, Java!");
System.out.println(message);

This explicitly creates a new string object in memory.

Common String Operations

1. Finding String Length

String text = "Java Programming";
System.out.println("Length: " + text.length());

2. Converting to Upper and Lower Case

String name = "Java";
System.out.println(name.toUpperCase()); // Output: JAVA
System.out.println(name.toLowerCase()); // Output: java

3. Concatenation (Joining Strings)

String firstName = "John";
String lastName = "Doe";
String fullName = firstName + " " + lastName;
System.out.println(fullName); // Output: John Doe

Or using the concat() method:

String fullName2 = firstName.concat(" ").concat(lastName);
System.out.println(fullName2);

4. Checking if Two Strings are Equal

String str1 = "Java";
String str2 = "java";
System.out.println(str1.equals(str2)); // false
System.out.println(str1.equalsIgnoreCase(str2)); // true

5. Extracting a Substring

String sentence = "Welcome to Java";
String sub = sentence.substring(11);
System.out.println(sub); // Output: Java

6. Replacing Characters in a String

String original = "Java is fun";
String replaced = original.replace("fun", "awesome");
System.out.println(replaced); // Output: Java is awesome

7. Splitting a String

String data = "apple,banana,grape";
String[] fruits = data.split(",");
for (String fruit : fruits) {
    System.out.println(fruit);
}

8. Checking if a String Contains a Word

String text = "Learning Java is fun!";
System.out.println(text.contains("Java")); // true

String Immutability

In Java, strings are immutable, meaning their values cannot be changed once created.
Any modification results in a new string being created.

Example:

String word = "Hello";
word = word + " World"; // Creates a new string
System.out.println(word);

Mutable Strings: `StringBuilder` and `StringBuffer`

If frequent modifications are needed, use StringBuilder or StringBuffer:

Using `StringBuilder`

StringBuilder sb = new StringBuilder("Hello");
sb.append(" World");
System.out.println(sb.toString());

Using `StringBuffer` (Thread-Safe)

StringBuffer sbf = new StringBuffer("Java");
sbf.append(" Programming");
System.out.println(sbf.toString());

Conclusion

Strings are essential in Java programming, used in almost every application. Understanding how to create, manipulate, and optimize them improves performance and code efficiency.

← Arrays

Conditional Statements →

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