You can also set auto completion to open automatically while typing.
Go to Preferences > Java > Editor > Content Assist and write .abcdefghijklmnopqrstuvwxyz in the Auto activation triggers for Java field.
eclipse (ALT+/)
1.选择Eclipse菜单栏中的Window->preferences；
2.选择General->keys;
3.在右侧中间的窗体中点击word completion后再点击remove binding,在下方的binding中随便（例如"Alt+."）输入一个快捷键；
4.然后选择Content Assist点击Remove binding，在binding中输入Alt+/；
在 Window - Preferences - General - Keys 内
1、把word completion的快捷键设置alt+C
2、把Content Assist的快捷键由ctrl+space改成alt+/