nullpointerexception

来源： https://stackoverflow.com/questions/63095257/how-to-avoid-java-lang-nullpointerexception-in-my-code

来源： https://stackoverflow.com/questions/63095257/how-to-avoid-java-lang-nullpointerexception-in-my-code

来源： https://stackoverflow.com/questions/40450023/caused-by-java-lang-nullpointerexception-attempt-to-invoke-virtual-method-int

来源： https://stackoverflow.com/questions/40450023/caused-by-java-lang-nullpointerexception-attempt-to-invoke-virtual-method-int

来源： https://stackoverflow.com/questions/63666863/how-to-call-methods-in-springboot

来源： https://stackoverflow.com/questions/63666863/how-to-call-methods-in-springboot

来源： https://stackoverflow.com/questions/63766504/having-issues-getting-the-drawing-done-on-this

来源： https://stackoverflow.com/questions/63766504/having-issues-getting-the-drawing-done-on-this

来源： https://stackoverflow.com/questions/63766504/having-issues-getting-the-drawing-done-on-this

问题 This question's answers are a community effort . Edit existing answers to improve this post. It is not currently accepting new answers or interactions. What are Null Pointer Exceptions ( java.lang.NullPointerException ) and what causes them? What methods/tools can be used to determine the cause so that you stop the exception from causing the program to terminate prematurely? 回答1: When you declare a reference variable (i.e. an object) you are really creating a pointer to an object. Consider