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Java Interview Questions and Answers
What is the difference between the
Reader/Writer class hierarchy and the InputStream/OutputStream class
hierarchy?
The Reader/Writer class hierarchy is character-oriented, and the
InputStream/OutputStream class hierarchy is byte-oriented.
What classes of exceptions may be caught by
a catch clause?
A catch clause can catch any exception that may be assigned to the
Throwable type. This includes the Error and Exception types.
What is the difference between throw and throws keywords?
The throw keyword denotes a statement that causes an exception to be
initiated. It takes the Exception object to be thrown as argument. The
exception will be caught by an immediately encompassing try-catch
construction or propagated further up the calling hierarchy.
The throws keyword is a modifier of a method that designates that
exceptions may come out of the method, either by virtue of the method
throwing the exception itself or because it fails to catch such
exceptions that a method it calls may throw.
If a class is declared without any access modifiers, where may the
class be accessed?
A class that is declared without any access modifiers is said to have
package or friendly access. This means that the class can only be
accessed by other classes and interfaces that are defined within the
same package.
What is the Map interface?
The Map interface replaces the JDK 1.1 Dictionary class and is used
associate keys with values.
Does a class inherit the constructors of its super class?
A class does not inherit constructors from any of its superclasses.
Name primitive Java types.
The primitive types are byte, char, short, int, long, float, double, and
Boolean.
Which class should you use to obtain design information about an
object?
The Class class is used to obtain information about an object's design.
How can a GUI component handle its own events?
A component can handle its own events by implementing the required
event-listener interface and adding itself as its own event listener.
How are the elements of a GridBagLayout organized?
The elements of a GridBagLayout are organized according to a grid.
However, the elements are of different sizes and may occupy more than
one row or column of the grid. In addition, the rows and columns may
have different sizes.
What advantage do Java's layout managers provide over traditional
windowing systems?
Java uses layout managers to lay out components in a consistent manner
across all windowing platforms. Since Java's layout managers aren't tied
to absolute sizing and positioning, they are able to accommodate
platform-specific differences among windowing systems.
What are the problems faced by Java programmers who don't use layout
managers?
Without layout managers, Java programmers are faced with determining how
their GUI will be displayed across multiple windowing systems and
finding a common sizing and positioning that will work within the
constraints imposed by each windowing system.
What is the difference between static and non-static variables?
A static variable is associated with the class as a whole rather than
with specific instances of a class. Non-static variables take on unique
values with each object instance.
What is the difference between the paint() and repaint() methods?
The paint() method supports painting via a Graphics object. The
repaint() method is used to cause paint() to be invoked by the AWT
painting thread.
What is the purpose of the File class?
The File class is used to create objects that provide access to the
files and directories of a local file system.
Why would you use a synchronized block vs. synchronized method?
Synchronized blocks place locks for shorter periods than synchronized
methods.
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