On String Operation Time Complexity

Interview Question In
the following classes, is the time complexity of method1 and method2 the same? why.

public class Test {
	public static final int MB = 1024 * 1024;
	public static final long TIMES = 500000000L;

	public static void main(String[] args) throws InterruptedException {
		method1();
		method2();
	}
//From the bytecode point of view, method1 repeats new StringBuilder
Then append, obviously not efficient. JIT optimization is excluded here.
	public static void method1() {
		String s = "";
		for (int i = 0; i < 100; i++) {
			s += "a";
		}

		System.out.println(s);
	}

	public static void method2() {
		// //b
		StringBuilder sb = new StringBuilder();
		for (int i = 0; i < 100; i++) {
			sb.append("a");
		}
		System.out.println(sb.toString());
	}

}

My answer at the time was that it should be the same, because I really couldn't find a way to say they were different. But there must be a reason for the interviewer to ask this question. I only analyze it from the aspect of efficiency. For example, method1 will be done through StringBuilder, which is not as good as the latter method2. Later, the interviewer corrected the question and said that it was considered from the time complexity. I told him directly, all I could see was the same, maybe method2 would be better. The interviewer didn't seem very satisfied.

When I came back, I started to look at the source code, and it felt unreliable. Later, I saw that someone analyzed it with bytecode. You can see how the compiler translates. It has been confirmed that it is the same as what I think. The bytecode is as follows:

Compiled from "Test.java"
public class Test extends java.lang.Object{
public static final int MB;

public static final long TIMES;

public Test();
  Code:
   0:	aload_0
   1:	invokespecial	#16; //Method java/lang/Object."<init>":()V
   4:	return

public static void main(java.lang.String[])   throws java.lang.InterruptedException;
  Code:
   0:	invokestatic	#27; //Method method1:()V
   3:	invokestatic	#30; //Method method2:()V
   6:	return

public static void method1();
  Code:
   0:	ldc	#35; //String
   2:	astore_0
   3:	iconst_0
   4: istore_1
   5:	goto	31
   8:	new	#37; //class java/lang/StringBuilder
   11: dup
   12:	aload_0
   13:	invokestatic	#39; //Method java/lang/String.valueOf:(Ljava/lang/Object;)Ljava/lang/String;
   16:	invokespecial	#45; //Method java/lang/StringBuilder."<init>":(Ljava/lang/String;)V
   19:	ldc	#48; //String a
   21:	invokevirtual	#50; //Method java/lang/StringBuilder.append:(Ljava/lang/String;)Ljava/lang/StringBuilder;
   24:	invokevirtual	#54; //Method java/lang/StringBuilder.toString:()Ljava/lang/String;
   27:	astore_0
   28: here 1, 1
   31:	iload_1
   32: bipush 100
   34:	if_icmplt	8
   37:	getstatic	#58; //Field java/lang/System.out:Ljava/io/PrintStream;
   40:	aload_0
   41:	invokevirtual	#64; //Method java/io/PrintStream.println:(Ljava/lang/String;)V
   44:	return

public static void method2();
  Code:
   0:	new	#37; //class java/lang/StringBuilder
   3: dup
   4:	invokespecial	#73; //Method java/lang/StringBuilder."<init>":()V
   7:	astore_0
   8:	iconst_0
   9: istore_1
   10:	goto	23
   13:	aload_0
   14:	ldc	#48; //String a
   16:	invokevirtual	#50; //Method java/lang/StringBuilder.append:(Ljava/lang/String;)Ljava/lang/StringBuilder;
   19:	pop
   20: here 1, 1
   23:	iload_1
   24: bipush 100
   26:	if_icmplt	13
   29:	getstatic	#58; //Field java/lang/System.out:Ljava/io/PrintStream;
   32:	aload_0
   33:	invokevirtual	#54; //Method java/lang/StringBuilder.toString:()Ljava/lang/String;
   36:	invokevirtual	#64; //Method java/io/PrintStream.println:(Ljava/lang/String;)V
   39:	return

}