Comment by za3faran

Rust:

    concat/string           time:   [77.801 ns 78.103 ns 78.430 ns]
                            change: [+0.0275% +0.3169% +0.6169%] (p = 0.03 < 0.05)
                            Change within noise threshold.
    formatted/string        time:   [31.471 ns 31.569 ns 31.699 ns]
                            change: [+0.1277% +0.3915% +0.6788%] (p = 0.01 < 0.05).   
                            Change within noise threshold.

Java

    Benchmarks.concat      string  avgt   15   8.632 ± 0.105  ns/op
    Benchmarks.format      string  avgt   15  64.971 ± 1.406  ns/op

Java's string concat is faster than rust's offerings.