public static void main(String[] args) {
	long start = System.currentTimeMillis();
	for (int i = 0; i < 1000000; i++) {
		String a = i + "";
	}
	System.out.println(System.currentTimeMillis() - start);
	long start1 = System.currentTimeMillis();
	for (int i = 0; i < 1000000; i++) {
		String b = String.valueOf(i);
	}
	System.out.println(System.currentTimeMillis() - start1);
	long start2 = System.currentTimeMillis();
	for (int i = 0; i < 1000000; i++) {
		String c = Integer.toString(i);
	}
	System.out.println(System.currentTimeMillis() - start2);
}
 

程式最後執行結果： 
125
35
35

可以看出直接加雙引號的轉換是呼叫方法轉換的三倍耗時，儘量少使用直接加空字串來轉換數字