Introduction to Strings in Java

What are Strings?

  • Definition of strings: Strings are sequences of characters, represented by the String class in Java.
  • Explanation of string literals: String literals are sequences of characters enclosed in double quotes (").
  • Declaration and initialization of strings: Examples of string declaration and initialization:


String str1 = "Hello, World!"; // Using string literal String str2 = new String("Java"); // Using new keyword

String Class Overview

  • Explanation of the String class in Java: The String class provides methods for manipulating strings and represents immutable sequences of characters.
  • Immutable nature of strings: Once a string object is created, it cannot be changed.

String Creation and Initialization

Creating Strings

  • Using string literals:

String greeting = "Hello";

  • Using the new keyword:

String message = new String("Welcome");

String Initialization

  • Direct assignment:

String firstName = "John";

  • Using constructor methods:

char[] nameArray = {'M', 'a', 'r', 'y'};

String lastName = new String(nameArray);

String Methods and Operations

Basic String Operations

  • Concatenation (+ operator):

String fullName = firstName + " " + lastName;

  • String length (length() method):

int length = fullName.length();

String Methods

  • charAt(int index):

char firstChar = fullName.charAt(0);

  • indexOf(String str):

int index = fullName.indexOf("Mary");

  • substring(int beginIndex) and substring(int beginIndex, int endIndex):

String subString1 = fullName.substring(6); // "Smith" String subString2 = fullName.substring(0, 4); // "John"

  • toUpperCase() and toLowerCase():

String upperCaseFullName = fullName.toUpperCase();

String lowerCaseLastName = lastName.toLowerCase();

  • equals(Object obj) and equalsIgnoreCase(String anotherString):

boolean isEqual = fullName.equals(lastName); boolean isEqualIgnoreCase = fullName.equalsIgnoreCase("mary smith");

  • startsWith(String prefix) and endsWith(String suffix):

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boolean startsWithJohn = fullName.startsWith("John"); boolean endsWithSmith = fullName.endsWith("Smith");

  • trim():

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String paddedString = " Java "; String trimmedString = paddedString.trim(); // "Java"

  • replace(char oldChar, char newChar):

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String replacedString = fullName.replace('J', 'K'); // "Kohn Smith"

  • split(String regex):

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String[] parts = fullName.split(" "); // {"John", "Smith"}

  • valueOf():

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int number = 123; String numberString = String.valueOf(number); // "123"

String Manipulation


  • Using the + operator:

String message = "Hello, " + name;

  • Using the concat() method:

String newMessage = message.concat("!");

String Comparison

  • Using equals() and equalsIgnoreCase():

boolean isEqual = message.equals(newMessage); boolean isEqualIgnoreCase = message.equalsIgnoreCase("hello, world!");

Searching and Manipulation

  • Using indexOf(), lastIndexOf(), startsWith(), and endsWith():

int index = fullName.indexOf("John");

boolean startsWith = fullName.startsWith("Jo");

  • Using substring():

String lastName = fullName.substring(5);

Modifying Strings

  • Immutable nature of strings: Strings cannot be modified after creation.
  • Using StringBuilder and StringBuffer for mutable string operations:

StringBuilder builder = new StringBuilder();

builder.append("Java"); builder.append(" is");

builder.append(" awesome");

String result = builder.toString(); // "Java is awesome"

String Formatting

String Formatting

  • Using printf():

System.out.printf("The value of x is %d and y is %f", x, y);

  • Using String.format():

String formattedString = String.format("The value of x is %d", x);

Best Practices and Tips

String Pool and Memory Management

  • Understanding string pooling: String literals are stored in a string pool to conserve memory.
  • Implications for memory management: Strings in the string pool are reused to minimize memory consumption.

Efficiency and Performance

  • Choosing the right string manipulation methods: Use StringBuilder for efficient string concatenation.
  • Using StringBuilder for concatenation of large strings:

StringBuilder builder = new StringBuilder();

for (int i = 0; i < 1000; i++) {



String result = builder.toString();

Understanding Java Strings is fundamental for Java programmer. Mastery of string manipulation and utilization of string methods can significantly enhance the functionality and efficiency of Java applications.