当成功把jdk1.6安装到 /usr/java，并且配置好了系统环境变量?

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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;

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Java代码 ?

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.??

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切换默认jdk版本执行

1.?

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Java代码 ?

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???

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2. Remove the old empty java environment?

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Java代码 ?

1. #?rm?-f?/usr/bin/java???
2. #?rm?-f?/usr/bin/javac???
3. #?rm?-f?/etc/alternatives/java???
4. #?rm?-f?/etc/alternatives/javac）???

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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

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Java代码 ?

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)?