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A.PRIMARY KEY (部门号) NOT NULL UNIQUE
B.PRIMARY KEY (部门名) UNIQUE
C.FOREIGN KEY (负责人) REFERENCES 员工 (姓名)
D.FOREIGN KEY (负责人) REFERENCES 员工 (员工号)
A.
B.
C.
D.
KV结构的集合,在处理null值的存储上有细微的区别,下列哪些说法是正确的:A.TreeMap的key不可以为nullB.TreeMap的key可以为nullC.ConcurrentHashMap的key可以为nullD.ConcurrentHashMap的value可以为null
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6、设P11接按键key0,则,测试按键释放的语句为()A.if(key0==0)B.if(key0==1)C.key=0D.key=1
下列表达正确的是()A.if(key=0)B.if(key==0)C.for(key=0)D.while(key=0);
设P11接按键key0,则,测试按键释放的语句为()A.if(key0==0)B.if(key0==1)C.key=0D.key=1
6.设按键key按下时,产生低电平0。实现key按下时,key_state 置1的程序段是()A.if(key == 1) { delay(200); if(key == 1) key_state = 1; }B.if(key == 0) { delay(200); if(key == 0) key_state = 1; }C.while(key == 0) { delay(200); while (key == 0) key_state = 1; }D.while(key == 1) { delay(200); while (key == 1) key_state = 1; }
等待按键按下后松开的语句是() A. while(key=0); B. if(key==0); C. while(key==0); D. if(key=0);
HashTable允许key和vaule为null。