Java String

Java Strings

In this tutorial, we will cover the basics of Java Strings. You will learn how to create strings, use various methods of the String class, and see examples of how these concepts are applied in real-world scenarios. Whether you are a beginner or an experienced Java developer, this tutorial is a valuable resource for understanding the fundamentals of Java Strings.

Java Strings are a sequence of characters that represent text. They are an important data type in Java and are used in many applications. The built-in class for working with strings in Java is java.lang.String.

For example, consider a scenario where you need to store a person's name. In Java, you can use a string to store the person's name like this:

String name = "John Doe";

The string "John Doe" is now stored in a variable called name, which can be used in your program to represent the person's name. You can also manipulate the string using various methods provided by the java.lang.String class, such as concatenating strings, searching for substrings, or converting strings to different formats.

Creating a String in Java

Creating a String in Java is straightforward and can be done in a few different ways.

1) Using String literals: The most common way to create a string in Java is to use string literals, which are sequences of characters enclosed in double quotes:

String name = "John Doe";

In this example, the string "John Doe" is stored in a variable called name.

2)Using the String constructor: Another way to create a string in Java is to use the String constructor:

String name = new String("John Doe");

In this example, we are using the new operator to create a new instance of the String class. This method is less commonly used compared to using string literals, as string literals provide a more concise and efficient way to create strings.

Once you have created a string, you can use various methods of the String class to manipulate and work with it. In the next sections of this tutorial, we will explore some of these methods in more detail.

Java String Operations

Java provides several methods for manipulating and working with strings, which are defined in the java.lang.String class. Some of the most commonly used methods are:

1) length() method: Returns the number of characters in the string.

class Main {
  public static void main(String[] args) {

    // create a string
    String greet = "Hello! World";
    System.out.println("String: " + greet);

    // get the length of greet
    int length = greet.length();
    System.out.println("Length: " + length);
  }
}

Output:

String: Hello! World
Length: 12

In the above example, the length() method calculates the total number of characters in the string and returns it.

2) concat() method: Joins two strings together to form a new string.

String firstName = "John";
String lastName = "Doe";
String fullName = firstName.concat(lastName);

In this example, the concat() method is used to join the strings firstName and lastName to form the string fullName, which is "John Doe".

3) charAt() method: Returns the character at the specified index in the string.

String name = "John Doe";
char firstInitial = name.charAt(0);

In this example, the charAt() method is used to return the first character of the string name, which is 'J'.

These are just a few examples of the many methods available in the String class for working with strings in Java. In this tutorial, we will explore these methods and more in greater detail, and provide examples of how they can be used in real-world scenarios.

Escape character in Java Strings

In Java, an escape character is a special character that is used to indicate that the character following it should be treated differently. For example, the escape character \ can be used to insert a newline character in a string, or to escape quotes within a string.

Here are some common escape characters in Java:

1) \n: Newline character.

2) \t: Tab character.

3) \r: Carriage return character.

4) \\: Backslash character.

5) \": Double quote character.

6) \': Single quote character.

Here's an example of how escape characters can be used in a string in Java:

String message = "Hello,\nWelcome to the world of Java Strings!";

In this example, the newline character \n is used to insert a line break within the string message. When the string is printed, it will appear on two separate lines:

 

Hello,
Welcome to the world of Java Strings!

In Java, escape characters can be useful for formatting strings in specific ways, or for inserting special characters within a string. By understanding and using escape characters in your Java code, you can write more powerful and flexible string operations.

Java Strings are Immutable

In Java, a string is an object that represents a sequence of characters. One important property of strings in Java is that they are immutable, which means that once a string is created, its value cannot be changed. Instead, any operation that appears to modify a string actually creates a new string with the desired modification.

Here's an example of how this works in practice:

String name = "John Doe";
name = name.toUpperCase();

In this example, the toUpperCase() method is called on the string name, and the result is stored in a new string object. The original string name remains unchanged.

The immutability of strings in Java has several important implications:

1) Strings are safe to use as keys in hash maps and as elements in arrays. Since strings cannot be modified, there is no risk of their values changing unexpectedly and causing problems with hash code calculations or indexing.

2) Strings can be safely shared between multiple threads without the risk of data corruption. Since strings cannot be modified, there is no need to worry about synchronizing access to them.

3) Strings can be efficiently optimized by the Java virtual machine (JVM). Since strings cannot be modified, the JVM can optimize their storage and manipulation to reduce the amount of memory used and improve performance.

Overall, the immutability of strings in Java makes them a powerful and flexible data type for working with text data in your applications. By understanding and using strings effectively, you can write more robust and efficient Java code.

Methods of Java String

Here is a table of 20 commonly used methods in the Java String class:

Method	Description
length()	Returns the length of the string
charAt(int index)	Returns the character at the specified index
concat(String str)	Concatenates the specified string to the end of the current string
indexOf(String str)	Returns the index of the first occurrence of the specified string or -1 if the string is not found
lastIndexOf(String str)	Returns the index of the last occurrence of the specified string or -1 if the string is not found
substring(int startIndex)	Returns a new string that is a substring of the current string, starting from startIndex and continuing to the end of the string
substring(int startIndex, int endIndex)	Returns a new string that is a substring of the current string, starting from startIndex and ending at endIndex-1
toLowerCase()	Returns a new string that is a lowercase version of the current string
toUpperCase()	Returns a new string that is an uppercase version of the current string
trim()	Returns a new string with leading and trailing whitespaces removed
replace(char oldChar, char newChar)	Returns a new string with all occurrences of oldChar replaced with newChar
replace(CharSequence target, CharSequence replacement)	Returns a new string with all occurrences of the target sequence replaced with the replacement sequence
split(String regex)	Returns an array of strings, splitting the current string into substrings based on the specified regular expression
startsWith(String prefix)	Returns true if the string starts with the specified prefix
endsWith(String suffix)	Returns true if the string ends with the specified suffix
matches(String regex)	Returns true if the string matches the specified regular expression
contains(CharSequence s)	Returns true if the string contains the specified sequence of characters
equals(Object obj)	Returns true if the string is equal to the specified object
equalsIgnoreCase(String anotherString)	Returns true if the string is equal to the specified string, ignoring case differences
compareTo(String anotherString)	Compares two strings lexicographically, and returns an integer indicating their relative order.
compareToIgnoreCase(String str)	Compares two strings lexicographically, ignoring case differences, and returns an integer indicating their relative order.

In conclusion, Java strings are an integral part of the Java programming language, and understanding how to create, manipulate, and use them is essential for any Java programmer. From creating strings using literals or the new keyword, to the various methods available in the String class, the topics covered in this tutorial should provide a solid foundation for working with Java strings. Whether you are a beginner or an experienced Java programmer, it is always useful to have a good understanding of the basics, and the Java strings are no exception.