In Linux/*nix system, the input method may fail to activate to make inputs. This is normally caused by:

1. The input method (e.g., SCIM) hot key is conflicted with Java program. Change your input method's hot key.
2. The XIM module is not successfully loaded.  For this problem, take the SCIM as example, please try:
   1. Check the XIM's configuration, and the output should be 1
      
      1. export | grep XMODIFIER | grep "@im=SCIM" | wc -l
   2. Check the SCIM module, and the output should be bigger or equal to 1
      
      1. ps aux | grep "scim-launcher.*-f x11" | grep -v grep | wc -l
      1. The output should be greater or equal to 1. If not, try
      2. scim -d -c socket -f x11 -e socket

Reference:
[1] Java Chinese and input method, available at: http://linuxtoy.org/archives/java_chinese.html