Java String

String in Java

A string in Java is a sequence of characters used to represent text. It is one of the most used data types in programming and is essential for handling textual data. Here’s a comprehensive explanation of what a string is, its characteristics, and how it is used:

Creating a simple string with a value

String name = “Justin”;

Gets the number of characters in the string

int size = name.length(); //where size is a variable with int type and name.length the method to get the length of string name (Justin).
System.out.println(size); // Output will be 6

Joining 2 strings using concatenation format

String firstname = “Justin”;
String lastname = “bieber”;
System.out.println(firstname + ” ” + lastname); // Output will be Justin bieber

This line prints a concatenated string to the console. The + operator is used to concatenate the strings. Here, firstname + ” ” + lastname combines the strings with a space between Justin & bieber, resulting in “Justin bieber.”

Joining 3 strings using placeholder format

String firstname = “Justin”;
String middlename = “hudson”;
String lastname = “bieber”;

System.out.println(String.format(“%s %s”, firstname, lastname)); // Output will be Justin bieber
System.out.println(String.format(“%s %s %s”, firstname, middlename, lastname)); // Output will be Justin hudson bieber

%s is used as a placeholder for strings in String.format, with each subsequent argument replacing the respective placeholder.

Convert string to all uppercase characters

String name = “Justin”;
String capital = name.toUpperCase();
System.out.println(capital); // Output will be JUSTIN

Convert string to all lowercase characters

String name = “Justin”;
String lowercase = name.toLowerCase();
System.out.println(lowercase); // Output will be justin

Retrieves a substring from the string

String name = “Justin”;
String substring = name.substring(0, 4);
System.out.println(substring); // Output will be Just

The substring() method extracts a portion of the string. The first parameter (0) specifies the starting index, and the second parameter (4) specifies the length of the substring.

Character/Length

1

2

3

4

5

6

Index

0

1

2

3

4

5

Removes all starting and ending white-space characters

String name = ” Justin drake “;
String space = name.trim();
System.out.println(space); // Output will be “Justin drake”

The trim() method removes any leading and trailing spaces from the string.
It will remove the blank spaces marked in blue above

Determines whether a string contains a specified substring

String name = “Justin drake”;
boolean shortname = name.contains(“Justin”);
System.out.println(shortname); // Output will be true

Determines whether a string starts with a specified substring

String name = “Justin”;
boolean starting = name.startsWith(“Ju”);
System.out.println(starting); // Output will be true

Determines whether a string ends with a specified substring

String name = “Justin”;
boolean ending = name.endsWith(“!”);
System.out.println(ending); // Output will be false

Determines whether the value in the string is the same as the value mentioned in the equals() method

String name = “Justin”;
boolean value = name.equals(“Hello, World!”);
System.out.println(value); // Output will be false

Copies one string variable value to another string variable

String name = “Justin”;
String duplicate = new String(name);
System.out.println(duplicate); // Output will be Justin

Replaces words or characters in a string

String name = “Justin bieber”;
String changeword = name.replace(“Justin”, “Drake”);
String changecharacter = name.replace(‘b’, ‘B’);
System.out.println(changeword); // Output: Drake bieber
System.out.println(changecharacter); // Output: Justin BieBer

Insert a value into a string variable Java doesn’t have a direct Insert() method like C#. You can simulate this by combining substring and concatenation:
String name = “Justin”;
String newName = name.substring(0, 6) + ” bieber”;
System.out.println(newName); // Output: Justin bieber

The remove method Java doesn’t have a direct Remove() method like C#. You can achieve the same result using substring():
String name = “Justin drake”;
String shortened = name.substring(0, 5);
System.out.println(shortened); // Output will be Justi. It has taken first five characters in the name and removed rest of the characters.

Tasks:

1. Create a Simple String: Create a string variable called myName and assign it your name. Print the string to the console.
2. Get Length of String: Write a program to get the number of characters in the string myName and print the length.
3. Concatenation: Create two string variables firstName and lastName with your first and last names. Concatenate them using the + operator and print the result. Repeat the above step using string interpolation. Repeat the above step using placeholders.
4. Case Conversion: Convert the string myName to uppercase and print the result. Convert the string myName to lowercase and print the result.
5. Substring: Extract a substring from myName that includes the first three characters and print it. Extract the last three characters of myName and print them.
6. Trim: Create a string with leading and trailing white spaces and print it. Then, remove the white spaces using the trim method and print the result.
7. Contains: Check if the string myName contains a specified substring (e.g., your first name) and print the result.
StartsWith and EndsWith: Check if the string myName starts with your first name and print the result. Check if the string myName ends with your last name and print the result.
8. Equals: Create another string variable with the same value as myName and check if they are equal using the equals method. Print the result.
9. Copy: Copy the value of myName into another string variable called copiedName and print it.
10. Replace: Replace your first name in the string myName with another name and print the result. Replace all occurrences of a specific character in myName with another character and print the result.
11. Insert: Insert a middle name into the string myName at the appropriate position and print the result.
12. Remove: Remove the last name from the string myName and print the result.

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Frequently Asked Questions

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The String class in Java is used to represent a sequence of characters and is one of the most commonly used classes in Java. 

This course covers the basics of Java Strings, String methods, and operations such as concatenation, comparison, and manipulation.

Yes, the course is completely free and available online on Iqra Technology Academy.

It is designed for beginners who want to learn about Strings and their methods in Java.

Common methods include .length(), .charAt(), .substring(), .equals(), .compareTo(), .replace(), .toUpperCase(), and .toLowerCase().

Yes, the course provides practical examples for each method and operation covered.

Yes, the course teaches how to concatenate Strings using the + operator and the .concat() method.

Yes, it covers methods like .equals(), .equalsIgnoreCase(), and .compareTo() for comparing Strings.

The course explains the differences, focusing on immutability of String and mutability of StringBuilder.

The course explains how to use the .substring() method to extract parts of a String.

It is a comprehensive and free resource for learning Java String methods and operations, with practical examples to help beginners build a strong foundation in Java programming.