bash: javac: command not found...

1、

[root@PC3 yum.repos.d]# java -version
java version "1.7.0_51"
OpenJDK Runtime Environment (rhel-2.4.5.5.el7-x86_64 u51-b31)
OpenJDK 64-Bit Server VM (build 24.51-b03, mixed mode)

2、

[root@PC3 yum.repos.d]# yum list java*
Loaded plugins: langpacks, product-id, subscription-manager
This system is not registered to Red Hat Subscription Management. You can use subscription-manager to register.
Installed Packages
java-1.7.0-openjdk.x86_64                                         1:1.7.0.51-2.4.5.5.el7                                @anaconda/7.0
java-1.7.0-openjdk-headless.x86_64                                1:1.7.0.51-2.4.5.5.el7                                @anaconda/7.0
javapackages-tools.noarch                                         3.4.1-5.el7                                           @anaconda/7.0
Available Packages
java-1.6.0-openjdk.x86_64                                         1:1.6.0.0-6.1.13.1.el7                                rhel7
java-1.6.0-openjdk-devel.x86_64                                   1:1.6.0.0-6.1.13.1.el7                                rhel7
java-1.7.0-openjdk-devel.x86_64                                   1:1.7.0.51-2.4.5.5.el7                                rhel7
java-atk-wrapper.i686                                             0.30.4-5.el7                                          rhel7
java-atk-wrapper.x86_64                                           0.30.4-5.el7                                          rhel7
javamail.noarch                                                   1.4.6-8.el7                                           rhel7
javassist.noarch                                                  3.16.1-10.el7                                         rhel7

3、

[root@PC3 yum.repos.d]# yum install java-1.7.0-openjdk-devel.x86_64
Loaded plugins: langpacks, product-id, subscription-manager
This system is not registered to Red Hat Subscription Management. You can use subscription-manager to register.
Resolving Dependencies
--> Running transaction check
---> Package java-1.7.0-openjdk-devel.x86_64 1:1.7.0.51-2.4.5.5.el7 will be installed
--> Finished Dependency Resolution

Dependencies Resolved

=====================================================================================================================================
 Package                                  Arch                   Version                                 Repository             Size
=====================================================================================================================================
Installing:
 java-1.7.0-openjdk-devel                 x86_64                 1:1.7.0.51-2.4.5.5.el7                  rhel7                 9.1 M

Transaction Summary
=====================================================================================================================================
Install  1 Package

Total download size: 9.1 M
Installed size: 36 M
Is this ok [y/d/N]: y
Downloading packages:
Running transaction check
Running transaction test
Transaction test succeeded
Running transaction
  Installing : 1:java-1.7.0-openjdk-devel-1.7.0.51-2.4.5.5.el7.x86_64                                                            1/1
rhel7/productid                                                                                               | 1.6 kB  00:00:00
  Verifying  : 1:java-1.7.0-openjdk-devel-1.7.0.51-2.4.5.5.el7.x86_64                                                            1/1

Installed:
  java-1.7.0-openjdk-devel.x86_64 1:1.7.0.51-2.4.5.5.el7

Complete!

4、

[root@PC3 yum.repos.d]# javac -version
javac 1.7.0_51