当成功把jdk1.6安装到 /usr/java，并且配置好了系统环境变量
执行 # java -version 时显示的不是你安装的jdk版本，而是其它版本如jdk1.4.2，是因为linux系统有默认的jdk，版本为1.4.2;
1 [root@ip-10-0-0-54 lib]# java -version 2 java version "1.4.2" 3 gij (GNU libgcj) version 4.1.2 20080704 (Red Hat 4.1.2-44) 4 5 Copyright (C) 2006 Free Software Foundation, Inc. 6 This is free software; see the source for copying conditions. There is NO 7 warranty; not even for MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.
切换默认jdk版本执行
1.
1 # cd /usr/bin 2 # ln -s -f /usr/java/jdk1.6.0_24/jre/bin/java 3 # ln -s -f /usr/java/jdk1.6.0_24/bin/javac
2.Remove the old empty java environment 去除旧的JDK 1.4.2
1 # rm -f /usr/bin/java 2 # rm -f /usr/bin/javac 3 # rm -f /etc/alternatives/java 4 # rm -f /etc/alternatives/javac
如果执行完1，查看 /usr/bin下的java properties，如果已经修改过来了，则步骤2不必再执行，命令行输入
# java –version
则可以看到jdk版本已经正常
1 java version "1.6.0_24" 2 Java(TM) SE Runtime Environment (build 1.6.0_24-b07) 3 Java HotSpot(TM) 64-Bit Server VM (build 19.1-b02, mixed mode)