我有 Debian GNU/Linux 6.0，apt 配置如下：
# squeeze
deb http://ftp.cz.debian.org/debian/ squeeze main contrib non-free
deb-src http://ftp.cz.debian.org/debian/ squeeze main contrib non-free
我想安装 Java 7，但是 apt 没有看到它：
apt-cache search openjdk
openjdk-6-dbg - Java runtime based on OpenJDK (debugging symbols)
openjdk-6-jdk - OpenJDK Development Kit (JDK)
openjdk-6-jre - OpenJDK Java runtime, using Hotspot JIT
怎么了？