fix compilation problem in openjdk7
fix compilation problem in openjdk7

bcambel/oss.io,meizhoubao/hackersome,bcambel/hackersome,meizhoubao/hackersome,bcambel/oss.io,bcambel/hackersome,bcambel/hackersome,bcambel/oss.io,meizhoubao/hackersome,meizhoubao/hackersome,bcambel/hackersome,bcambel/oss.io