异常处理

1)What is displayed on the console when running the following program?

class Test {

  public static void main (String[ ] args) {

    try {

      System.out.println("Welcome to Java");

    }

    finally {

      System.out.println("The finally clause is executed");

    }

  }

}

A)Welcome to Java followed by The finally clause is executed in the next line
B)Welcome to Java
C)The finally clause is executed
D)None of the above

无论异常是否发生，finally子句总会被执行

2)The following code causes Java to throw ________.
int number = Integer.MAX_VALUE + 1; 2) _______
A)Exception B)Error C)Throwable D)RuntimeException E)no exceptions

3)What is displayed on the console when running the following program?

class Test {

  public static void main (String[ ] args) {

    try {

      System.out.println("Welcome to Java");

      return;

    }

    finally {

      System.out.println("The finally clause is executed");

    }

  }

}

A)The finally clause is executed
B)Welcome to Java followed by The finally clause is executed in the next line
C)Welcome to Java
D)None of the above

在任何情况下finally块中的代码都会执行，即使finally子句中有一个return语句，finally块还是会被执行。

4)Which of the following is not an advantage of Java exception handling? 4) _______
A)Exception handling simplifies programming because the error-reporting and error-handling code can be placed at the catch block.
B)Java separates exception handling from normal processing tasks.
C)Exception handling makes it possible for the caller's caller to handle the exception.
D)Exception handling improves performance.

A，B，C都是异常处理的优点，但异常处理不能提升程序的性能

处理简化了编程，因为错误报告和错误处理代码可以放在catch块中。
Java将异常处理与普通的处理任务分开。
异常处理使调用方的调用方能够处理异常。

5)An instance of ________ describes programming errors, such as bad casting, accessing an out-of-bounds array, and numeric errors.. 5) _______
A)Error B)NumberFormatException C)Throwable D)RuntimeException E)Exception

Exception描述由你的程序和外部环境所引起的错误，这些错误能被程序捕获和处理。

6)Analyze the following code:

class Test {

  public static void main(String[ ] args)

    throws MyException {

    System.out.println("Welcome to Java");

  }

}

class MyException extends Error {

}

A)You should not declare a class that extends Error, because Error raises a fatal error that terminates the program.
B)The program has a compilation error.
C)You cannot declare an exception in the main method.
D)You declared an exception in the main method, but you did not throw it.

Error类不能被继承，Error描述的是内部系统错误，会引发致命错误，从而终止程序。

7)An instance of ________ are unchecked exceptions. (Choose all that apply.) 7) _______
A)NumberFormatException B)Throwable C)Error D)RuntimeException E)Exception

RuntimeException、Error以及它们的子类都称为unchecked exceptions 未经检查的异常

8)A method must declare to throw ________. 8) _______
A)unchecked exceptions B) Error C)RuntimeException D) checked exceptions

checked exceptions检查性异常，编译器会强制程序员检查并通过try-catch块来处理它们，或者在方法头进行声明

9)What is displayed on the console when running the following program?

class Test {

  public static void main(String[ ] args) {

    try {

      System.out.println("Welcome to Java");

      int i = 0;

      int y = 2/i;

      System.out.println("Welcome to Java");

    }

    finally {

      System.out.println("End of the block");

    }

    System.out.println("End of the block");

  }

}

A)The program displays Welcome to Java and End of the block, and then terminates because of an unhandled exception.
B)The program displays Welcome to Java two times followed by End of the block two times.
C)The program displays Welcome to Java two times followed by End of the block.
D)The program displays Welcome to Java three times followed by End of the block.

存在ArithmeticException算数异常没有处理unhandled exception

10)What exception type does the following program throw?

public class Test {

  public static void main(String[ ] args) {

    String s = "abc";

    System.out.println(s.charAt(3));

  }

}

A)No exception
B)ArithmeticException
C)StringIndexOutOfBoundsException
D)ArrayIndexOutOfBoundsException
E)ClassCastException

注意这里是String类型

11)An instance of ________ describes system errors. If this type of error occurs, there is little you can do beyond notifying the user and trying to terminate the program gracefully. 11) ______
A)Throwable B)Error C)RuntimeException D)Exception E)NumberFormatException

Error描述的是内部系统错误，会引发致命错误，从而终止程序。

12)What is displayed on the console when running the following program?

class Test {

  public static void main(String[ ] args) {

    try {

      System.out.println("Welcome to Java");

      int i = 0;

      int y = 2/i;

      System.out.println("Welcome to HTML");

    }

    finally {

      System.out.println("The finally clause is executed");

    }

  }

}

A)Welcome to Java followed by The finally clause is executed in the next line.
B)The program displays three lines: Welcome to Java, Welcome to HTML, The finally clause is executed.
C)Welcome to Java. D)None of the above.

13)What exception type does the following program throw?

public class Test {

  public static void main(String[ ] args) {

    Object o = new Object();

    String d = (String)o;

  }

}

A)ArithmeticException
B)ArrayIndexOutOfBoundsException
C)ClassCastException
D)No exception
E)StringIndexOutOfBoundsException

父类对象o不是子类对象d的一个实例，不能进行转换，否则会出现ClassCastException

14)What exception type does the following program throw?

public class Test {

  public static void main(String[ ] args) {

    Object o = null;

    System.out.println(o.toString());

  }

}

A)ArrayIndexOutOfBoundsException
B)ClassCastException
C)NullPointerException
D)ArithmeticException
E)StringIndexOutOfBoundsException

toStrinfg()返回一个描述该对象的字符串，而这里Object对象没有创建，会造成NullPointerException
15)What is wrong in the following program?

class Test {

  public static void main (String[ ] args) {

    try {

      System.out.println("Welcome to Java");

     }

  }

}

A)You cannot have a try block without a catch block.
B)You cannot have a try block without a catch block or a finally block.
C)Nothing is wrong.
D)A method call that does not declare exceptions cannot be placed inside a try block.

try之后必须要有catch或者finally

16)An instance of ________ describes the errors caused by your program and external circumstances. These errors can be caught and handled by your program. 16) ______
A)Throwable B)RuntimeException C)Error D)Exception E)NumberFormatException

Exception描述由你的程序和外部环境所引起的错误，这些错误能被程序捕获和处理。

17)Analyze the following code:

class Test {

  public static void main(String[ ] args) {

    try {

      String s = "5.6";

      Integer.parseInt(s); // Cause a NumberFormatException

      int i = ;

      int y =  / i;

    }

    catch (Exception ex) {

      System.out.println("NumberFormatException");

    }

    catch (RuntimeException ex) {

      System.out.println("RuntimeException");

    }

  }

}

A)The program displays NumberFormatException.
B)The program displays RuntimeException.
C)The program has a compilation error.
D)The program displays NumberFormatException followed by RuntimeException.

注意：

这里有两个catch子句，并且Exception还是RuntimeException的父类，这样RutimeException是多余的，会造成编译错误的。

Unreachable catch block for RuntimeException. It is already handled by the catch block for Exception

18)What exception type does the following program throw?

public class Test {

  public static void main(String[ ] args) {

    System.out.println(1 / 0);

  }

}

A)StringIndexOutOfBoundsException
B)ArrayIndexOutOfBoundsException
C)ArithmeticException
D)No exception
E)ClassCastException

19)What is displayed on the console when running the following program?

class Test {

  public static void main(String[ ] args) {

    try {

      method();

      System.out.println("After the method call");

    }

    catch (NumberFormatException ex) {

      System.out.println("NumberFormatException");

    }

    catch (RuntimeException ex) {

      System.out.println("RuntimeException");

    }

  }

  static void method() {

    String s = "5.6";

    Integer.parseInt(s); // Cause a NumberFormatException

    int i = 0;

    int y = 2 / i;

    System.out.println("Welcome to Java");

  }

}

A)The program displays NumberFormatException followed by RuntimeException.
B)The program displays RuntimeException.
C)The program has a compilation error.
D)The program displays NumberFormatException followed by After the method call.
E)The program displays NumberFormatException.

抛出算数异常2/0后没有可以捕获的catch，造成程序中断

20)What is displayed on the console when running the following program?

class Test {

  public static void main(String[ ] args) {

    try {

      System.out.println("Welcome to Java");

      int i = 0;

      double y = 2.0 / i;

      System.out.println("Welcome to HTML");

    }

    finally {

      System.out.println("The finally clause is executed");

    }

  }

}

A)Welcome to Java.
B)The program displays three lines: Welcome to Java, Welcome to HTML, The finally clause is executed.
C)Welcome to Java followed by The finally clause is executed in the next line.
D)None of the above.

注意上面是浮点数

21)What exception type does the following program throw?

public class Test {

  public static void main(String[ ] args) {

    int[ ] list = new int[5];

    System.out.println(list[5]);

  }

}

A)ClassCastException
B)ArithmeticException
C)No exception
D)ArrayIndexOutOfBoundsException
E)StringIndexOutOfBoundsException

数组越界

22)Analyze the following code:

class Test {

  public static void main(String[ ] args) {

    try {

      int zero = 0;

      int y = 2/zero;

      try {

        String s = "5.6";

        Integer.parseInt(s); // Cause a NumberFormatException

      }

      catch(Exception e) {

      }

    }

    catch(RuntimeException e) {

      System.out.println(e);

    }

  }

}

A)The program has a compilation error because Exception appears before RuntimeException.
B)A try-catch block cannot be embedded inside another try-catch block.
C)A good programming practice is to avoid nesting try-catch blocks, because nesting makes programs difficult to read. You can rewrite the program using only one try-catch block.
D)None of the above.

一个好的程序是避免嵌套try-catch块，因为嵌套会使程序难于阅读。可以仅使用一个try-catch块重写程序。

23)Analyze the following program.

class Test {

  public static void main(String[ ] args) {

    try {

      String s = "5.6";

      Integer.parseInt(s); // Cause a NumberFormatException

      int i = 0;

      int y = 2 / i;

      System.out.println("Welcome to Java");

    }

    catch (Exception ex) {

      System.out.println(ex);

    }

  }

}

A)The program has a compilation error.
B)An exception is raised due to 2 / i;
C)The program compiles and runs without exceptions.
D)An exception is raised due to Integer.parseInt(s);

注意到这里的NumberFormatException实现抛出来的，之后会将正常的执行流程给中断掉，也就是说会跳过try块剩余的语句。

24)What is displayed on the console when running the following program?

class Test {

  public static void main(String[ ] args) {

    try {

      method();

      System.out.println("After the method call");

    }

    catch (RuntimeException ex) {

      System.out.println("RuntimeException");

    }

    catch (Exception ex) {

      System.out.println("Exception");

    }

  }

  static void method() throws Exception {

    try {

      String s = "5.6";

      Integer.parseInt(s); // Cause a NumberFormatException

      int i = 0;

      int y = 2 / i;

      System.out.println("Welcome to Java");

    }

    catch (RuntimeException ex) {

      System.out.println("RuntimeException");

    }

    catch (Exception ex) {

      System.out.println("Exception");

    }

  }

}

A)The program displays Exception followed by RuntimeException.
B)The program displays RuntimeException twice.
C)The program has a compilation error.
D)The program displays RuntimeException followed by After the method call.
E)The program displays Exception twice.

注意这道题的说法，是在调用方法结束之后显示异常，不要把这个After the method call当做打印信息的“After the method call”

25)What is displayed on the console when running the following program?

class Test {

  public static void main(String[ ] args) {

    try {

      System.out.println("Welcome to Java");

      int i = 0;

      int y = 2/i;

      System.out.println("Welcome to Java");

    }

    catch (RuntimeException ex) {

      System.out.println("Welcome to Java");

    }

    finally {

      System.out.println("End of the block");

    }

  }

}

A)The program displays Welcome to Java two times.
B)The program displays Welcome to Java two times followed by End of the block.
C)The program displays Welcome to Java three times.
D)The program displays Welcome to Java three times followed by End of the block.

ArithmeticException是RuntimeException的子类，子类的实例总是父类的实例

26)What is displayed on the console when running the following program?

class Test {

  public static void main(String[ ] args) {

    try {

      System.out.println("Welcome to Java");

      int i = 0;

      int y = 2/i;

      System.out.println("Welcome to Java");

    }

    catch (RuntimeException ex) {

      System.out.println("Welcome to Java");

    }

    finally {

      System.out.println("End of the block");

    }

    System.out.println("End of the block");

  }

}

A)The program displays Welcome to Java two times followed by End of the block.
B)The program displays Welcome to Java two times followed by End of the block two times.
C)The program displays Welcome to Java three times followed by End of the block.
D)You cannot catch RuntimeException errors.

27)What is displayed on the console when running the following program?

class Test {

  public static void main(String[ ] args) {

    try {

      method();

      System.out.println("After the method call");

    }

    catch (RuntimeException ex) {

      System.out.println("RuntimeException");

    }

    catch (Exception ex) {

      System.out.println("Exception");

    }

  }

  static void method() throws Exception {

    try {

      String s = "5.6";

      Integer.parseInt(s); // Cause a NumberFormatException

      int i = 0;

      int y = 2 / i;

      System.out.println("Welcome to Java");

    }

    catch (NumberFormatException ex) {

      System.out.println("NumberFormatException");

      throw ex;

    }

    catch (RuntimeException ex) {

      System.out.println("RuntimeException");

    }

  }

}

A)The program has a compilation error.
B)The program displays NumberFormatException followed by After the method call.
C)The program displays NumberFormatException followed by RuntimeException.
D)The program displays NumberFormatException twice.

NumberFormatException

RuntimeException

注意这里先捕获

28)A Java exception is an instance of ________. 28) ______
A)RuntimeException B)Error C)NumberFormatException D)Exception E)Throwable

异常exception的根类是java.lang.Throwable

29)What exception type does the following program throw?

public class Test {

  public static void main(String[ ] args) {

    Object o = null;

    System.out.println(o);

  }

}

A)No exception
B)ArrayIndexOutOfBoundsException
C)StringIndexOutOfBoundsException
D)NullPointerException
E)ArithmeticException

30)Which of the following statements are true? (Choose all that apply.) 30) ______
A)You use the keyword throws to declare exceptions in the method heading.
B)If a checked exception occurs in a method, it must be either caught or declared to be thrown from the method.
C)A method may declare to throw multiple exceptions.
D)To throw an exception, use the key word throw.

文本IO

31)Which class do you use to write data into a text file? 2) _______
A)File B) System C)Scanner D) PrintWriter

32)Which class do you use to read data into a text file? 10) ______
A)Scanner B) System C)PrintWriter D) File

使用Scanner类从文件中读取文本数据，使用 PrintWriter 类向文本文件写入数据

33)Which of the following statements are true? 12) ______
A)If a file (e.g., c:\temp.txt) does not exist, new File("c:\\temp.txt") creates a new file named c:\temp.txt.
B)If a directory (e.g., c:\liang) does not exist, new File("c:\liang") creates a new directory named c:\liang.
C)If a file (e.g., c:\temp.txt) does not exist, new File("c:\\temp.txt") returns null.
D)If a directory (e.g., c:\liang) does not exist, new File("c:\liang") returns null.
E)None of the above.

34)Which class contains the method for checking whether a file exists? 14) ______
A)System B) Scanner C)File D) PrintWriter

15)Which of the following statements creates an instance of File on Window for the file c:\t.txt?
A)new File("c:\txt.txt")  B) new File("c:\\txt.txt")
C)new File("c://txt.txt") D) new File("c:/txt.txt")

在java中，反斜杠是一个特殊的字符，应该写成\\形式

35)Which of the following returns the path separator character? 18) ______
A)File.separatorChar
B)File.pathSeparatorChar
C)File.pathSeparator
D)File.separator
E)None of the above.

36)Which method can be used to write data? 24) ______
A)exist B) print C) close D) rename

37)Which method can be used to create an output object for file temp.txt? (Choose all that apply.)
A)new PrintWriter("temp.txt")
B)new PrintWriter(new File("temp.txt"))
C)new PrintWriter(File("temp.txt"))
D)new PrintWriter(temp.txt)

38)Suppose you enter 34.3, the ENTER key, 57.8, the ENTER key, 789, the ENTER key. Analyze the following code.

Scanner scanner = new Scanner(System.in);

int value = scanner.nextDouble();

int doubleValue = scanner.nextInt();

String line = scanner.nextLine();

A)After the last statement is executed, intValue is 34.
B)After the last statement is executed, line contains characters '7 ', '8 ', '9'.
C)After the last statement is executed, line contains character  '\n '.
D)The program has a runtime error because 34.3 is not an integer.
E)After the last statement is executed, line contains characters '7', '8', '9', '\n'.

39)Which method can be used to create an input object for file temp.txt? 31) ______
A)new Scanner("temp.txt")
B)new Scanner(temp.txt)
C)new Scanner(File("temp.txt"))
D)new Scanner(new File("temp.txt"))

40)What are the reasons to create an instance of the File class? (Choose all that apply.) 37) ______
A)To delete the file.
B)To read/write data from/to a file
C)To rename the file.
D)To obtain the properties of the file such as whether the file can be read, written, or is hidden.
E)To determine whether the file exists.

41)Which method can be used to read a whole line from the file? 43) ______
A)nextDouble B) nextLine C)next D) nextInt

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