Exploring Strings in Java: Your Ultimate Core Java Interview Guide - Part 1

Creating Strings

Strings can be created using two methods

• String literal: Simply enclosing text within double quotes, like?"Hello Dinuka".
• Using the?new?keyword: Instantiating a new String object, like?new String("Hello Dinuka").

Difference Between String Literal and?new?Keyword

String literal

• Utilizes a string pool in memory.
• If the string already exists in the pool, the same reference is used.

new?keyword

• Creates a new object in the heap memory every time, regardless of whether the string exists in the pool.
• Consumes more memory compared to the string literal approach.

Immutability of Strings

• Strings in Java are immutable, meaning they cannot be changed once created.

This is because:

• It ensures thread safety.
• Prevents unintended modifications by other parts of the program.

Overcoming Immutability

• While strings are inherently immutable, you can change the reference to point to a different string.

To enforce immutability

• Declare the string variable as?final.
• Use string buffers or string builders for mutable string operations.
• String buffers are thread-safe but slower due to synchronisation.
• String builders are faster but not thread-safe.

Commonly Used String Methods

• length(): Returns the length of the string.
• charAt(int index): Returns the character at the specified index.
• substring(int beginIndex): Returns a substring starting from the specified index.
• substring(int beginIndex, int endIndex): Returns a substring between the specified begin and end indices.
• toLowerCase(): Converts all characters in the string to lowercase.
• toUpperCase(): Converts all characters in the string to uppercase.
• indexOf(String str): Returns the index of the first occurrence of the specified substring.
• lastIndexOf(String str): Returns the index of the last occurrence of the specified substring.
• replace(char oldChar, char newChar): Replaces all occurrences of a specified character with another character.
• startsWith(String prefix): Checks if the string starts with the specified prefix.
• endsWith(String suffix): Checks if the string ends with the specified suffix.

Happy Coding!