SCJP真题库更新4
QUESTION 10
Given the exhibit:
What is the result??
A. short Long
B. SHORT LONG
C. Compilation fails
D. An exception is thrown at runtime
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Answer: ( C )?? 向上就近原则.
第20行的go(z)将会依序找go(int i), go(long l),go(float f), go(double d) 或go(Integer i)方法.但是并不会自动向上转型Long然后再呼叫go(Long n),这种依顺序向上找的特性只会发生在对应端基本资料型别的情况下,
参考大纲：面向对象 — 重载； 实用API — 自动封包、拆包
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QUESTION 11
Given the exhibit:
* d is valid , non-null Date object
* df is a valid, non-null DateFormat object set to the current local
What outputs the current local's country name and the appropriate version of D's date??
A. Locale loc = Locale.getLocal ( );
System.out printIn (loc.getDisplayCountry ( )
B. Locale loc = Locale.getDefault ( );
System.out printIn (loc.getDisplayCountry ( ) + " " +df. format (d) );
C. Locale loc = Locale.getLocal ( );
System.out printIn (loc.getDisplayCountry ( ) + " " +df. setDateFormat (d) );
D. Locale loc = Locale.getDefault ( );
System.out printIn (loc.getDisplayCountry ( ) + " " +df.seDateFormat (d) );
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Answer: ( B )
A? Locale类没有getLocal()方法,编译错误
B? 正确
C? 错误Locale类没有getLocal( )方法? DateFormat没有setDateFormat( )方法,编译错误
D? DateFormat没有setDateFormat( )方法 编译错误
参考大纲：实用API — java.util包 和java.text包
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QUESTION 12
Given the exhibit:
What is the result??
A. Compilation fails.
B. An exception is thrown at runtime
C. The code executes and prints " running"
D. The code executes and prints "runningrunning"
E. The code executes and prints "runningrunningrunning
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Answer: ( E )
t.run（）调用main主线程去执行2-4行的run(),就是一次普通的方法调用 ;t.start()表示起用thread线程负责去执行2-4行的run();?? 把2-4行的代码改为:
public void run(){
??????? String threadName=Thread.currentThread().getName();
System.out.println(threadName+”:running”);
}
这样就可以看出是谁调用了run()了,显示如下:
main : running
main : running
Thread-o : running
参考大纲：多线程
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QUESTION 13------------仔细看看
Exhibit:
Which two are possible results? (choose two)?
A. 0,2,4,4,6,8,10,6, ??
B. 0,2,4,6,8,10,2,4,
C. 0,2,4,6,8,10,12,14, ??
D. 0,0,2,2,4,4,6,6,8,8,10,10,12,12,14,14,
E. 0,2,4,6,8,10,12,14,0,2,4,6,8,10,12,14,
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Answer: ( A, C)
A 第一个线程循环到第三遍使得x等于4，并执行完第8句后挂起（此时current也是4）；第二个线程开始执行，执行完以后第一个线程接着执行最后一次循环，打印6
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C 两个线程依次执行
参考大纲：多线程
