Make sure you have you have the latest version of JRE installed in your system.
If the problem still persists then ,the reason being the JRE’s of your system might not be added to the project under consideration. Please follow the steps below .
1) Eclipse Tool Bar>Window>Preferences> Java>Installed Jre’s.
2) You should be seeing the path of the JRE installed.Now copy the location of installed JREs
3) Close the window.
4) Select your Project>Rt ck >Properties>Java Build Path
5) In Libraries tab > clk Add library button
6) In Add Library Window>Select JRE System Library option>next
7) In JRE System Library window >clk on Installed JREs > (you should be able to see the path of the insatlled JREs) Select the JRE path
8) Finish
OR
Other Things done if the above did not solve the problem : - A ) Eclipse Tool bar > Project >Clean
