Files.mismatch()
Compare two files efficiently without loading them into memory.
Code Comparison
✕ Java 8
// Compare two files byte by byte byte[] f1 = Files.readAllBytes(path1); byte[] f2 = Files.readAllBytes(path2); boolean equal = Arrays.equals(f1, f2); // loads both files entirely into memory
✓ Java 12+
long pos = Files.mismatch(path1, path2); // -1 if identical // otherwise: position of first difference
Why the modern way wins
Memory-efficient
Doesn't load entire files into byte arrays.
Pinpoints difference
Returns the exact byte position of the first mismatch.
One call
No manual byte array comparison logic.
Old Approach
Manual Byte Compare
Modern Approach
Files.mismatch()
Since JDK
12
Difficulty
beginner
JDK Support
Files.mismatch()
Available
Widely available since JDK 12 (March 2019)
How it works
Files.mismatch() returns the position of the first byte that differs, or -1 if the files are identical. It reads lazily and short-circuits on the first difference.