How to Concatenate Strings Without Extra Allocation in Java

What are the methods for concatenating strings in Java without causing additional memory allocation?

StringBuilder sb = new StringBuilder();
sb.append("Hello").append(" ").append("World!");
String result = sb.toString();

String concatenation in Java traditionally involves creating new string objects, leading to memory allocation overhead. However, using efficient approaches like StringBuilder can help perform concatenations without unnecessary allocations.

StringBuilder sb = new StringBuilder();
sb.append("First part");
sb.append(" second part");
String concatenated = sb.toString();

Causes

• Using the `+` operator causes each concatenation to create a new String object.
• Java's String class is immutable, which means any modification results in a new object being created.

Solutions

• Utilize `StringBuilder` or `StringBuffer`, which are mutable classes that allow for efficient string modifications without extra memory allocation.
• Use `String.join()` for concatenating multiple strings with a delimiter without additional overhead.

Mistake: Using the `+` operator in a loop to concatenate strings, leading to performance issues.

Solution: Instead, initialize a StringBuilder outside the loop and append within the loop.

Mistake: Not preallocating StringBuilder capacity when the expected size is known, leading to multiple reallocations.

Solution: Specify the initial capacity of StringBuilder to minimize resizing: `StringBuilder sb = new StringBuilder(100);`.