How Does Java\'s Operator Achieve String Concatenation?

Understanding String Concatenation in Java: The Magic Behind the Operator

In Java, the operator can be used to concatenate strings, even though String is a class. However, upon examining the String.java source code, one might wonder how this operation is implemented.

This apparent violation of object orientation is resolved by the compiler's optimization. When Java encounters the operator with strings, it does the following:

5.1.11. String Conversion

• The Java compiler converts "x = " x; into a StringBuilder internally.
• It then uses the StringBuilder.append(int) method to "add" the integer to the string.

15.18.1. Optimization of String Concatenation

• The Java compiler may further optimize the process, directly converting primitive types to strings without creating wrapper objects.
• It may also use a StringBuffer to reduce the number of intermediate String objects created.

Compiler Optimization
The optimized code generated by the compiler for string concatenation resembles the following:

new StringBuilder(cip).append(ciop).toString();

This illustrates how the compiler transforms the operator into a StringBuilder.

In summary, the operator for string concatenation is a shorthand notation for the more verbose StringBuilder idiom. The compiler optimizes this operation to enhance performance by minimizing unnecessary object creation and providing efficient string handling capabilities.

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