Core Java Interview Question Page 15

Question: What invokes a thread's run() method?

Answer: After a thread is started, via its start() method or that of the Thread class, the JVM invokes the thread's run() method when the thread is initially executed.

Question: What is the difference between the Boolean & operator and the && operator?

Answer: If an expression involving the Boolean & operator is evaluated, both operands are evaluated. Then the & operator is applied to the operand. When an expression involving the && operator is evaluated, the first operand is evaluated. If the first operand returns a value of true then the second operand is evaluated. The && operator is then applied to the first and second operands. If the first operand evaluates to false, the evaluation of the second operand is skipped.

Question: Name three subclasses of the Component class.

Answer: Box.Filler, Button, Canvas, Checkbox, Choice, Container, Label, List, Scrollbar, or TextComponent

Question: What is the GregorianCalendar class?

Answer: The GregorianCalendar provides support for traditional Western calendars.

Question: Which Container method is used to cause a container to be laid out and redisplayed?

Answer: validate()

Question: What is the purpose of the Runtime class?

Answer: The purpose of the Runtime class is to provide access to the Java runtime system.

Question: How many times may an object's finalize() method be invoked by the garbage collector?

Answer: An object's finalize() method may only be invoked once by the garbage collector.

Question: What is the purpose of the finally clause of a try-catch-finally statement?

Answer: The finally clause is used to provide the capability to execute code no matter whether or not an exception is thrown or caught.

Question: What is the argument type of a program's main() method?

Answer: A program's main() method takes an argument of the String[] type.

Question: Which Java operator is right associative?

Answer: The = operator is right associative.

Question: What is the Locale class?

Answer: The Locale class is used to tailor program output to the conventions of a particular geographic, political, or cultural region.

Question: Can a double value be cast to a byte?

Answer: Yes, a double value can be cast to a byte.

Question: What is the difference between a break statement and a continue statement?

Answer: A break statement results in the termination of the statement to which it applies (switch, for, do, or while). A continue statement is used to end the current loop iteration and return control to the loop statement.

Question: What must a class do to implement an interface?

Answer: It must provide all of the methods in the interface and identify the interface in its implements clause.

Question: What method is invoked to cause an object to begin executing as a separate thread? 0

Answer: The start() method of the Thread class is invoked to cause an object to begin executing as a separate thread.

Question: Name two subclasses of the TextComponent class.

Answer: TextField and TextArea 1

Question: What is the advantage of the event-delegation model over the earlier event-inheritance model?

Answer: The event-delegation model has two advantages over the event-inheritance model. First, it enables event handling to be handled by objects other than the ones that generate the events (or their containers). This allows a clean separation

between a component's design and its use. The other advantage of the event-delegation model is that it performs much better in applications where many events are generated. This performance improvement is due to the fact that the event-delegation model does not have to repeatedly process unhandled events, as is the case of the event-inheritance model. 2