`concat()` vs ` `: Which Java String Concatenation Method is More Efficient?

String Concatenation: Dissecting 'concat()' vs ' ' Operator

The ' ' operator and the 'concat()' method, both employed for string concatenation, may seem interchangeable at first glance, but their underlying mechanisms and behaviors differ.

Under the Hood

The 'concat()' method is a String class method that непосредственно (literally) appends another string to the original one. On the other hand, the ' ' operator delegates concatenation to the StringBuilder class which is more efficient when dealing with multiple string manipulations.

Performance Differences

While the 'concat()' method is more restrictive in its input acceptance, it is generally faster for simple concatenation tasks. However, for complex or repeated concatenations, StringBuilder's approach proves superior in performance.

Example:

Analyzing the following Java code using the javap decompiler reveals the true nature of the ' ' operator:

public String cat(String a, String b) {
    a += b;
    return a;
}

The decompiled bytecode demonstrates that ' ' translates to the following:

a = new StringBuilder()
    .append(a)
    .append(b)
    .toString();

Conclusion

While the 'concat()' method appears streamlined, StringBuilder ultimately triumphs in terms of efficiency, especially when dealing with numerous string concatenations. It's worth noting that performance may vary based on recent JVM optimizations and HotSpot JVM intrinsics.

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