Attempt to invoke interface method 'int java.util.List.size()'

Question

安卓程序编译通过，但是出现java.lang.NullPointerException: Attempt to invoke interface method 'int java.util.List.size()' on a null object reference问题，且在模拟器上运行后显示停止运行

java.lang.NullPointerException: Attempt to invoke interface method 'int java.util.List.size()' on a null object reference