Strings, Exceptions, and Files

Question 1

How do you change the case of a String?

Answer 1

String s = “string”;
s.toLowerCase();
s.toUpperCase();

Question 2

What does String1.compareTo(String2) do?

Answer 2

it tells you which is first in “alphabetical order”. “Less” or “greater” is determined by the numeric codes (ASCII or Unicode) of the characters in that position. Uppercase is always less than lowercase

Question 3

How could you find one String within another?

Answer 3

string1.indexOf(string2);

Question 4

How can you remove leading/trailing whitespace from a String?

Answer 4

s.trim();

Question 5

How could you find what characters are between two indices?

Answer 5

String1.substring(start, end)

start is the position of the first character you want
end is the position of the first character you don’t want

Question 6

What does String[] split(String) do?

Answer 6

break up a String into an array of Strings at the positions of the given substring
“Test 12 34”.split(“ “) gives {“Test”, “12”, “34”}

Question 7

What are Exceptions?

Answer 7

represent problems that arise during execution, which a program might want to deal with. Exceptions are objects that give information about what went wrong and where in the program it went wrong.

Question 8

What are some examples of exceptions?

Answer 8

• 5/0 gives an Arithmetic Exception
• array[-1] = 0 gives an
  ArrayIndexOutOfBoundsException
• Integer.parseInt(“Not a number”) gives a NumberFormatException

Question 9

What are the methods that every exception object has?

Answer 9

• String getMessage() - find more about what happened
• void printStackTrace() - print out where the program was at the time this exception object was created
• String toString() - the name of the exception and its message

Question 10

What are Errors in Java

Answer 10

As opposed to Exceptions, Errors are more serious problems that a program is not supposed to manage/handle. When it happens, the program will terminate with a description of the error.

Question 11

What happens when you use an Exception?

Answer 11

When something goes wrong, you can “throw” an exception. This object is now automatically returned up the stack, immediately terminating all of these methods until it hits something that “catches” it.

Question 12

How do you use an Exception in a method?

Answer 12

all methods that throw an exception or call a method that does this have “throws Exception” at the end of the signature unless the method catches the exception itself.

Question 13

What is the format of a try-catch?

Answer 13

try {
… statements
}
catch(TypeOfException e) {
… do this if an exception happens
}
catch(OtherTypeOfException ae) { … }
finally {
… do this every time, whether try successfully completed or an exception was thrown and caught
}
… continue unless some un-caught exception occurs

Question 14

What are RuntimeExceptions?

Answer 14

unchecked exceptions. You don’t need to catch them, or declare in your method signature that it could throw them. RuntimeExceptions are thrown when the programmer makes a mistake and calls a method incorrectly. They happen during runtime

Question 15

What are checked exceptions?

Answer 15

Types of exceptions that must be handled wherever they may occur in your program; otherwise, your program will not compile

Question 16

What type of exception should you check for when using a fileReader?

Answer 16

FileNotFoundException
(java.io)

Question 17

What type of exception should you check for when parsing strings?

Answer 17

NumberFormatException
(java.lang)

Question 18

What type of exception should you check for when writing files?

Answer 18

IOException
(java.io)

Question 19

How do you read input from a file?

Answer 19

FileReader fileReader = new FileReader(filename);
Scanner in = new Scanner(fileReader);
in.nextLine();
in.close();

Question 20

How do you write input to a file?

Answer 20

FileWriter fileWriter = new FileWriter(filename);
BufferedWriter out = new BufferedWriter(fileWriter);
out.write(“”);
out.close();