Quiz ECE122 #1 Open books, open notes, No computer. Question 1: Which of the following is NOT right for Java programming language? 1. 2. 3. 4. Object oriented Platform dependent Garbage collected Multi-threaded
Answer
Weve mentioned that Java is platform-INDEPENDENT several times. This is one reason Java is so popular to use in web pages and also why it is so easy for us to allow you to use your home computers. So, by process of elimination, the answer must be 2. If youre interested in the other choices 1 Java is Object oriented. This means you design your code around data, and decide what operations you can perform on that data. (you'll soon see that one giveaway is the use of the word "class". Objects are instances of classes) 3 Garbage collected. This means that any memory you allocate will automatically be reclaimed by the system when your program no longer needs it. The non-garbage collected language C requires the programmer to "free" any memory that that was gotten with "malloc", and C++ requires the programmer to "delete" any memory that was gotten with "new". 4 Multi threaded. This means a program can have multiple threads of control. For instance, a web server could assign a separate thread to each user connected to it . The code to handle a user can be written and executed more or less as if there were never more than a single user using the server, relying on Java to give each thread/user a fair share of the computer.
Question 2: How do you invoke a Java virtual machine in a window DOS window? 1. 2. 3. 4. javac jar java None of the above
Answer
The answer is 3, java. You use the java command to have your program run by a Java virtual machine. The jar program is used to package up
many java class files into a single jar file (something like the zip utility on Windows). The javac program is the Java Compiler (see the next question).
Question 3: What will java compiler NOT do? 1. 2. 3. 4. Turn Java source code into Byte code Create java class files Check syntax errors in the source code Turn all your code into one archive file
Answer
The answer is 4. The javac Java compiler will take your source code and create class files from it. Inside the class files, the instructions you wrote are stored in a simpler format called byte codes. The compiler can only create a class file if your source code is syntactically correct. As described in question 3, you use the jar command to create an archive file.
Question 4: Why do you need to set up classpath in Java environment? 1. So that the Java virtual machine can find the class files and byte codes to execute. 2. So that the operating system can find the Java virtual machine to start 3. So that the operating system can find javac location 4. So that the operating system can find path environment variable. Answer
The answer is 1. CLASSPATH is a special variable that the programs that come with the a Java installation use to find resources, such as class files, that are specific to Java. The PATH variable is used to find any programs you might want to run, on both Windows and Unix -- answers 2 and 3. The OS always has access to its PATH variable.
Question 5: Which of the following can be the starting method that the java virtual machine look for to execute a typical Java Program? 1. 2. 3. 4. public static void main(String[] asdf) public static void main() public static void main(String args) Any of the above.
Answer
The answer is 1. In order, the tokens in the signature mean
public -static -write for void -main -String[] asdf -will hold
is visible outside the class to other classes does not need an object instance (all methods we'll a while will be static) it does not return values any the special name the Java virtual machine will look for -- the method takes an array of String objects essentially declares a local variable named asdf that the arguments. The name can be anything.
Probably the most common confusion was to think that the parameter had to be called args. This is just a typical name for the parameter since it holds the arguments to the program. Also, people often overlooked that the [] characters are a required part of the signature. See Java 2, page 15.
Question 6: What are the valid values of a java boolean? 1. 2. 3. 4. number 1, 0 string "1", "0" true, false any of the above
Answer
The answer is 3. Booleans are only true or false.
Question 7: What is the result of such program segment? int i = 4; int j = 3; double d = (double) (i/j); System.out.println(d); 1. 2. 3. 4. 1.33333333 1.0 1 none of the above
Answer
The answer is 2. Expressions in parentheses are always evaluated before expressions outside parentheses, just as in the arithmetic you learned in school. So this expression means First divide the integer 4 by the integer 3 using the integer divide operation. This gives integer 1. The integer 1 is then cast to the double value 1.0 and assigned to d. The println method will display this as "1.0".
Question 8: Do I have to write a main method in every class I create? 1. Yes 2. No Answer
The answer is no. Every program you write must have at least one main method in some class, since thats where the program starts running, but not every class in the program needs one. In fact, usually there is exactly one main method. For instance, you've used the String class; it's a utility class representing a text string. It has no main method. See Head First Java, page 10
Question 9: Which one will output the following result? I like ECE122 1. System.out.print("I like"); System.out.println("ECE122"); 2. System.out.println("I like\tECE122"); 3. System.out.println("I like\n"); System.out.println("ECE122"); 4. System.out.println("I like\nECE122); Answer
The intended answer was 4, but because this statement accidentally did not have a double quote character to end string, that choice is not v...