java编程50题及答案，适用于java编程训练及蓝桥杯赛前练习-java programming 50 questions and answers for java programming before training exercises and Blue Bridge Cup

常用4×4矩阵按键程序，适合初学者学习理解单片机控制原理(Commonly used 4 * 4 matrix button program, suitable for beginners to learn how to understand SCM control principle)