11

  public java.lang.String x(java.lang.String);
    descriptor: (Ljava/lang/String;)Ljava/lang/String;
    flags: (0x0001) ACC_PUBLIC
    Code:
      stack=1, locals=2, args_size=2
         0: aload_1
         1: invokedynamic #27,  0             // InvokeDynamic #0:makeConcatWithConstants:(Ljava/lang/String;)Ljava/lang/String;
         6: areturn

8

  public java.lang.String x(java.lang.String);
    descriptor: (Ljava/lang/String;)Ljava/lang/String;
    flags: (0x0001) ACC_PUBLIC
    Code:
      stack=3, locals=2, args_size=2
         0: new           #13                 // class java/lang/StringBuilder
         3: dup
         4: ldc           #14                 // int 3
         6: invokespecial #18                 // Method java/lang/StringBuilder."<init>":(I)V
         9: ldc           #20                 // String zzz
        11: invokevirtual #24                 // Method java/lang/StringBuilder.append:(Ljava/lang/String;)Ljava/lang/StringBuilder;
        14: aload_1
        15: invokevirtual #24                 // Method java/lang/StringBuilder.append:(Ljava/lang/String;)Ljava/lang/StringBuilder;
        18: invokevirtual #28                 // Method java/lang/StringBuilder.toString:()Ljava/lang/String;
        21: areturn

readme.md

• これの説明 scala/scala#9556
• A.scala をScala 2.13.12で、それぞれJDK 11で --release:8 と --release:11 使ってcompileして、それを javap -v A した結果の一部

A.scala

class A {
  def x(y: String): String = "zzz" + y
}