把写内容过程中比较常用的内容段做个收藏，如下的内容段是关于Java中两个判断字符串是否为空的方法的执行效率比较的内容。

public class Test4

{ public static void main(String[] args) { long times = 999999999; String str = "";

long a1 = System.currentTimeMillis();      for (long i = 0; i < times && str.isEmpty(); i++)      {      }      long a2 = System.currentTimeMillis();      System.out.println("str.isEmpty() times: " + (a2 - a1));      long b1 = System.currentTimeMillis();      for (long i = 0; i < times && "".equals(str); i++)      {      }      long b2 = System.currentTimeMillis();      System.out.println(""".equals(str) times: " + (b2 - b1));  }  复制代码

}

输出结果如下：

str.isEmpty() times: 2735

"".equals(str) times: 10516

其实看下源码很快就发现问题所在

isEmpty()函数的源码

public boolean isEmpty() {

return count == 0; }

equals的源码

public boolean equals(Object anObject) {

if (this == anObject) { return true; } if (anObject instanceof String) { String anotherString = (String)anObject; int n = count; if (n == anotherString.count) { char v1[] = value; char v2[] = anotherString.value; int i = offset; int j = anotherString.offset; while (n-- != 0) { if (v1[i++] != v2[j++]) return false; } return true; } } return false; }