步骤：

1. Window->Preferences->Java->Installed JREs->Edit

2. Edit JRE->Default VM arguments->输入 -ea
   （ea：enable assertions）

   
   
   eclipse开启assert -step1

eclipse开启assert -step2

eclipse开启assert -step3

Eclipse: enable assertions
To globally set it as the default for everything:

1. Go to menu Window (if you are on Windows), or go to menu Eclipse (if you are on Mac). For Linux it might be something similar.
2. Go to Preferences.
3. Choose Java, and then Installed JREs from the left panel.
4. Select your JRE, and then click the Edit... button in the right panel.
5. In the Default VM arguments field, add -ea.