查看版本

         # java -version

         java version "1.4.2"

         gij (GNU libgcj) version 4.1.2 20080704 (Red Hat 4.1.2-48)

         Copyright (C) 2006 Free Software Foundation, Inc.

         This is free software; see the source for copying conditions.  There is NO

         warranty; not even for MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.

环境

Redhat5.5 x86_64

更新JDK版本：jdk-6u30-linux-x64.bin

1.拷贝jdk-6u30-linux-x64.bin到/tmp

2.赋予可执行权限

chmod a+x jdk-6u30-linux-x64.bin

3.执行

./jdk-6u30-linux-x64.bin

4.创建/usr/java目录

mkdir/usr/java

5.把/tmp/jdk1.6.0_30目录移动至/usr/java

mv /tmp/jdk1.6.0_30/usr/java

6.删除/usr/bin/java/usr/bin/javac

rm /usr/bin/java

rm /usr/bin/javac

7.执行

ln -s /usr/java/jdk1.6.0_30/bin/java/usr/bin/java

ln -s /usr/java/jdk1.6.0_30/bin/javac/usr/bin/javac

8.编译/etc/profile,在文件末尾加上

JAVA_HOME=/usr/java/jdk1.6.0_30

JRE_HOME=/usr/java/jdk1.6.0_30/jre

PATH=$PATH:$JAVA_HOME/bin:$JRE_HOME/bin

CLASSPATH=.:$JAVA_HOME/lib/dt.jar:$JAVA_HOME/lib/tools.jar:$JRE_HOME/lib:

export JAVA_HOME JRE_HOME PATHCLASSPATH

9.执行source /etc/profile

10. 查看版本

# java -version

      java version "1.6.0_30"

      Java(TM) SE Runtime Environment (build 1.6.0_30-b12)

      Java HotSpot(TM) 64-Bit Server VM (build 20.5-b03, mixed mode)

11. 编写helloWorld程序测试

# cat test.java

      public class test{

          public static void main(String[] args) {

                System.out.println("Hello World!");

          }

      }

       #javac test.java

       #java test

        Hello World!