Java StringConcat vs StringBuilder

gistfile1.txt

// StringConcat.java
public class StringConcat {
  public static void main(String[] args) {
    String abc = getA() + getB() + getC();
    System.out.println(abc);
  }

  private static String getA() {
    return "ABC";
  }

  private static String getB() {
    return "123";
  }

  private static String getC() {
    return "XYZ";
  }
}

Compiled from "StringConcat.java"
public class StringConcat {
  public StringConcat();
    Code:
       0: aload_0       
       1: invokespecial #1                  // Method java/lang/Object."<init>":()V
       4: return        

  public static void main(java.lang.String[]);
    Code:
       0: new           #2                  // class java/lang/StringBuilder
       3: dup           
       4: invokespecial #3                  // Method java/lang/StringBuilder."<init>":()V
       7: invokestatic  #4                  // Method getA:()Ljava/lang/String;
      10: invokevirtual #5                  // Method java/lang/StringBuilder.append:(Ljava/lang/String;)Ljava/lang/StringBuilder;
      13: invokestatic  #6                  // Method getB:()Ljava/lang/String;
      16: invokevirtual #5                  // Method java/lang/StringBuilder.append:(Ljava/lang/String;)Ljava/lang/StringBuilder;
      19: invokestatic  #7                  // Method getC:()Ljava/lang/String;
      22: invokevirtual #5                  // Method java/lang/StringBuilder.append:(Ljava/lang/String;)Ljava/lang/StringBuilder;
      25: invokevirtual #8                  // Method java/lang/StringBuilder.toString:()Ljava/lang/String;
      28: astore_1      
      29: getstatic     #9                  // Field java/lang/System.out:Ljava/io/PrintStream;
      32: aload_1       
      33: invokevirtual #10                 // Method java/io/PrintStream.println:(Ljava/lang/String;)V
      36: return        
}



// StringBuilder.java
public class StringBuilder {
  public static void main(String[] args) {
    String abc = new java.lang.StringBuilder().append(getA()).append(getB()).append(getC()).toString();
    System.out.println(abc);
  }

  private static String getA() {
    return "ABC";
  }

  private static String getB() {
    return "123";
  }

  private static String getC() {
    return "XYZ";
  }
}

Compiled from "StringBuilder.java"
public class StringBuilder {
  public StringBuilder();
    Code:
       0: aload_0       
       1: invokespecial #1                  // Method java/lang/Object."<init>":()V
       4: return        

  public static void main(java.lang.String[]);
    Code:
       0: new           #2                  // class java/lang/StringBuilder
       3: dup           
       4: invokespecial #3                  // Method java/lang/StringBuilder."<init>":()V
       7: invokestatic  #4                  // Method getA:()Ljava/lang/String;
      10: invokevirtual #5                  // Method java/lang/StringBuilder.append:(Ljava/lang/String;)Ljava/lang/StringBuilder;
      13: invokestatic  #6                  // Method getB:()Ljava/lang/String;
      16: invokevirtual #5                  // Method java/lang/StringBuilder.append:(Ljava/lang/String;)Ljava/lang/StringBuilder;
      19: invokestatic  #7                  // Method getC:()Ljava/lang/String;
      22: invokevirtual #5                  // Method java/lang/StringBuilder.append:(Ljava/lang/String;)Ljava/lang/StringBuilder;
      25: invokevirtual #8                  // Method java/lang/StringBuilder.toString:()Ljava/lang/String;
      28: astore_1      
      29: getstatic     #9                  // Field java/lang/System.out:Ljava/io/PrintStream;
      32: aload_1       
      33: invokevirtual #10                 // Method java/io/PrintStream.println:(Ljava/lang/String;)V
      36: return        
}