Strings & Text

Java Program to Reverse a String (StringBuilder & Two Pointers)

Reverse strings in Java efficiently using StringBuilder and in-place char array two-pointer swapping.

Java Source Code

Editable code sample with line numbers

Java

Expected Output

When this program is compiled and executed, the terminal outputs:

Original: ZenCompiler Online Java IDE
StringBuilder: EDI avaJ enilnO relipmoCneZ
Two Pointers:  EDI avaJ enilnO relipmoCneZ

How the Code Works

Java strings are immutable objects backed by a byte/char array. Concatenating with + in a loop creates multiple garbage objects. Using StringBuilder or converting to char[] allows direct, high-performance in-memory manipulation.

Time Complexity

O(N)

Space Complexity

O(N) for mutable buffer

Key Takeaways & Best Practices

Never concatenate strings in loops; use StringBuilder.
String.toCharArray() allows indexed in-place swapping.

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