字符串串联分配有效吗？

该特定示例将由编译器内联：

String a = "a";String b = "bb";String c = "ccc";String some = a + "t" + b + "t" + c;

Java
9+将使用带有makeConcatWithConstants的invokedynamic来内联此代码，以使其高效。根据

javap -v

Code:  stack=3, locals=5, args_size=1     0: ldc#2       // String a     2: astore_1     3: ldc#3       // String bb     5: astore_2     6: ldc#4       // String ccc     8: astore_3     9: aload_1    10: aload_2    11: aload_3    12: invokedynamic #5,  0   // InvokeDynamic #0:makeConcatWithConstants:(Ljava/lang/String;Ljava/lang/String;Ljava/lang/String;)Ljava/lang/String;    17: astore        4    19: return

但是，如果

a

b

c

final String a = "a";final String b = "bb";final String c = "ccc";String some = a + "t" + b + "t" + c;

并将

some

Code:  stack=1, locals=5, args_size=1     0: ldc#2       // String a     2: astore_1     3: ldc#3       // String bb     5: astore_2     6: ldc#4       // String ccc     8: astore_3     9: ldc#5       // String atbbtccc    11: astore        4    13: return

在其他情况下，例如

for

StringBuilder