Exception handling (I) -- null pointer and array index out of bounds

NullPointerException

The most common errors encountered . use debug Step by step jump elimination , Sometimes the parentheses are misplaced , Maybe the parameter in the method is wrong , So you should check carefully when writing , Try to avoid errors caused by null pointer exceptions .

• while After the cycle judgment, you should enter for loop , The error in the position of the brackets leads to the final judgment result of null, Null pointer exception

• Call in object getGameId() Method , Comparison is equal , Wrong book player.equals(gameId) Caused null pointer exception

It took me a long time to find out , Only later did I find out that it was if Sentence judgment player2 Have been to null 了 , So call playerDao.addPlayer（） I can't add this empty , It is a new entry player

ArrayIndexOutOfBoundsException

The element format does not follow