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);