Why doesn't the Java compiler concatenate string literals if they appear after a variable?

Question

I have the following test code: ``` public class StringLiteralTest { static void testPrefix() { int i = 0; String prefixConcat = "a" + "b" + i; } static void testSuffix() { int i = 0; String suffixConcat = i + "c" + "d"; } } ``` The generated bytecode is: ``` Compiled from "StringLiteralTest.java" public class StringLiteralTest { public StringLiteralTest(); Code: 0: aload_0 1: invokespecial #8 // Method java/lang/Object."":()V 4: return static void testPrefix(); Code: 0: iconst_0 1: istore_0 2: new #15 // class java/lang/StringBuilder 5: dup 6: ldc #17 // String ab 8: invokespecial #19 // Method java/lang/StringBuilder."":(Ljava/lang/String;)V 11: iload_0 12: invokevirtual #22 // Method java/lang/StringBuilder.append:(I)Ljava/lang/StringBuilder; 15: invokevirtual #26 // Method java/lang/StringBuilder.toString:()Ljava/lang/String; 18: astore_1 19: return static void testSuffix(); Code: 0: iconst_0 1: istore_0 2: new #15 // class java/lang/StringBuilder 5: dup 6: iload_0 7:…

Accepted Answer

Because the string concatenation operator (+) is syntactically left associative:

For example, the expression:

```
a + b + c
```

is always regarded as meaning:

```
(a + b) + c
```

Admittedly, if `b` and `c` are strings, the expression is equivalent to `a + (b + c)`. So a compiler could do what you suggest in that specific situation, but it is not mandated by the specification...

Why doesn't the Java compiler concatenate string literals if they appear after a variable?

Solution

Problem