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I am searching for a package of openjdk but i can't find it, every time gives me this response " sudo apt-get install openjdk-7-jdk
Reading package lists... Done
Building dependency tree
Reading state information... Done Package openjdk-7-jdk is not available, but is referred to by another package. This may mean that the package is missing, has been obsoleted, or is only available from another source
E: Package 'openjdk-7-jdk' has no installation candidate" how to solve this ?