关于JDK8中的字符串拼接示例详解

public static void main(String[] args) {
 String result = "";
 result += "some more data";
 System.out.println(result);
 }

Code:
 0: aload_0  // Push 'this' on to the stack
 1: invokespecial #1 // Invoke Object class constructor
    // pop 'this' ref from the stack
 4: return  // Return from constructor

 public static void main(java.lang.String[]);
 Code:
 0: ldc  #2 // Load constant #2 on to the stack
 2: astore_1  // Create local var from stack (pop #2)
 3: new  #3 // Push new StringBuilder ref on stack
 6: dup  // Duplicate value on top of the stack
 7: invokespecial #4 // Invoke StringBuilder constructor
    // pop object reference
 10: aload_1  // Push local variable containing #2
 11: invokevirtual #5 // Invoke method StringBuilder.append()
    // pop obj reference + parameter
    // push result (StringBuilder ref)
 14: ldc  #6 // Push "some more data" on the stack
 16: invokevirtual #5 // Invoke StringBuilder.append
    // pop twice, push result
 19: invokevirtual #7 // Invoke StringBuilder.toString:();
 22: astore_1  // Create local var from stack (pop #6)
 23: getstatic #8 // Push value System.out:PrintStream
 26: aload_1  // Push local variable containing #6
 27: invokevirtual #9 // Invoke method PrintStream.println()
    // pop twice (object ref + parameter)
 30: return  // Return void from method

public static void main(String[] args) {
 String result = "";
 for (int i = 0; i < 10; i++) {
  result += "some more data";
 }
 System.out.println(result);
 }

Code:
 0: aload_0  // Push 'this' on to the stack
 1: invokespecial #1 // Invoke Object class constructor
    // pop 'this' ref from the stack
 4: return  // Return from constructor

 public static void main(java.lang.String[]);
 Code:
 0: ldc  #2 // Load constant #2 on to the stack
 2: astore_1  // Create local var from stack, pop #2
 3: iconst_0  // Push value 0 onto the stack
 4: istore_2  // Pop value and store it in local var
 5: iload_2  // Push local var 2 on to the stack
 6: i2d  // Convert int to double on
    // top of stack (pop + push)
 7: ldc2_w  #3 // Push constant 10e6 on to the stack
 10: dcmpg  // Compare two doubles on top of stack
    // pop twice, push result: -1, 0 or 1
 11: ifge  40 // if value on top of stack is greater
    // than or equal to 0 (pop once)
    // branch to instruction at code 40
 14: new  #5 // Push new StringBuilder ref on stack
 17: dup  // Duplicate value on top of the stack
 18: invokespecial #6 // Invoke StringBuilder constructor
    // pop object reference
 21: aload_1  // Push local var 1 (empty String)
    // on to the stack
 22: invokevirtual #7 // Invoke StringBuilder.append
    // pop obj ref + param, push result
 25: ldc  #8 // Push "some more data" on the stack
 27: invokevirtual #7 // Invoke StringBuilder.append
    // pop obj ref + param, push result
 30: invokevirtual #9 // Invoke StringBuilder.toString
    // pop object reference
 33: astore_1  // Create local var from stack (pop)
 34: iinc  2, 1 // Increment local variable 2 by 1
 37: goto  5 // Move to instruction at code 5
 40: getstatic #10 // Push value System.out:PrintStream
 43: aload_1  // Push local var 1 (result String)
 44: invokevirtual #11 // Invoke method PrintStream.println()
    // pop twice (object ref + parameter)
 47: return  // Return void from method

String result = "";
for (int i = 0; i < 10; i++) {
 StringBuilder tmp = new StringBuilder();
 tmp.append(result);
 tmp.append("some more data");
 result = tmp.toString();
}
System.out.println(result);