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Java Interview Questions and Answers
What is an object's lock and which objects
have locks?
An object's lock is a mechanism that is used by multiple threads to
obtain synchronized access to the object. A thread may execute a
synchronized method of an object only after it has acquired the object's
lock. All objects and classes have locks. A class's lock is acquired on
the class's Class object.
What is the Dictionary class?
The Dictionary class provides the capability to store key-value pairs.
How are the elements of a BorderLayout organized?
The elements of a BorderLayout are organized at the borders (North,
South, East, and West) and the center of a container.
What is the % operator?
It is referred to as the modulo or remainder operator. It returns the
remainder of dividing the first operand by the second operand.
When can an object reference be cast to an interface reference?
An object reference be cast to an interface reference when the object
implements the referenced interface.
What is the difference between a Window and a Frame?
The Frame class extends Window to define a main application window that
can have a menu bar.
Which class is extended by all other classes?
The Object class is extended by all other classes.
Can an object be garbage collected while it is still reachable?
A reachable object cannot be garbage collected. Only unreachable objects
may be garbage collected.. Is the ternary operator written x : y ? z or x ? y : z ?
It is written x ? y : z.
What is the difference between the Font and FontMetrics classes?
The FontMetrics class is used to define implementation-specific
properties, such as ascent and descent, of a Font object.
How is rounding performed under integer division?
The fractional part of the result is truncated. This is known as
rounding toward zero.
What happens when a thread cannot acquire a lock on an object?
If a thread attempts to execute a synchronized method or synchronized
statement and is unable to acquire an object's lock, it enters the
waiting state until the lock becomes available.
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.
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 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 SimpleTimeZone class?
The SimpleTimeZone class provides support for a Gregorian calendar.
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 superclass?
A class does not inherit constructors from any of its super classes.
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