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Technical Interview Q & A PDF





Can an inner class declared inside of a method access local variables of this method? 

It's possible if these variables are final. 

What can go wrong if you replace &emp;&emp; with &emp; in the following code: String a=null; if (a!=null && a.length()>10) {...} 

A single ampersand here would lead to a NullPointerException.

What is the Vector class? 

The Vector class provides the capability to implement a growable array of objects 

What modifiers may be used with an inner class that is a member of an outer class? 

A (non-local) inner class may be declared as public, protected, private, static, final, or abstract. 

If a method is declared as protected, where may the method be accessed? 

A protected method may only be accessed by classes or interfaces of the same package or by subclasses of the class in which it is declared. What is an Iterator interface? 

The Iterator interface is used to step through the elements of a Collection. 

How many bits are used to represent Unicode, ASCII, UTF-16, and UTF-8 characters? 

Unicode requires 16 bits and ASCII require 7 bits. Although the ASCII character set uses only 7 bits, it is usually represented as 8 bits. UTF-8 represents characters using 8, 16, and 18 bit patterns. UTF-16 uses 16-bit and larger bit patterns. 

What's the main difference between a Vector and an ArrayList? 

Java Vector class is internally synchronized and ArrayList is not. 

What are wrapped classes? 

Wrapped classes are classes that allow primitive types to be accessed as objects. 

Does garbage collection guarantee that a program will not run out of memory? 

No, it doesn't. It is possible for programs to use up memory resources faster than they are garbage collected. It is also possible for programs to create objects that are not subject to garbage collection. 

What is the difference between preemptive scheduling and time slicing? 

Under preemptive scheduling, the highest priority task executes until it enters the waiting or dead states or a higher priority task comes into existence. Under time slicing, a task executes for a predefined slice of time and then reenters the pool of ready tasks. The scheduler then determines which task should execute next, based on priority and other factors. 

Name Component subclasses that support painting ?

The Canvas, Frame, Panel, and Applet classes support painting. 

What is a native method? 

A native method is a method that is implemented in a language other than Java. 

How can you write a loop indefinitely? 

for(;;)--for loop; while(true)--always true, etc. 

Can an anonymous class be declared as implementing an interface and extending a class? 

An anonymous class may implement an interface or extend a superclass, but may not be declared to do both. 

What is the purpose of finalization? 

The purpose of finalization is to give an unreachable object the opportunity to perform any cleanup processing before the object is garbage collected. 

When should the method invokeLater()be used? 

This method is used to ensure that Swing components are updated through the event-dispatching thread. 

How many methods in Object class? 

This question is not asked to test your memory. It tests you how well you know Java. Ten in total.

clone() 

equals() & hashcode() 

getClass() 

finalize() 

wait() & notify() 

toString() 

How does Java handle integer overflows and underflows? 

It uses low order bytes of the result that can fit into the size of the type allowed by the operation.

What is the numeric promotion? 

Numeric promotion is used with both unary and binary bitwise operators. This means that byte, char, and short values are converted to int values before a bitwise operator is applied. 

If a binary bitwise operator has one long operand, the other operand is converted to a long value

. The type of the result of a bitwise operation is the type to which the operands have been promoted. For example:

short a = 5;

byte b = 10;

long c = 15;

The type of the result of (a+b) is int, not short or byte. The type of the result of (a+c) or (b+c) is long. 

Is the numeric promotion available in other platform? 

Yes. Because Java is implemented using a platform-independent virtual machine, bitwise operations always yield the same result, even when run on machines that use radically different CPUs. 

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

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. Operator & has no chance to skip both sides evaluation and && operator does. If asked why, give details as above. 

When is the ArithmeticException throwQuestion: What is the GregorianCalendar class? 

The GregorianCalendar provides support for traditional Western calendars. 

What is the SimpleTimeZone class? 

The SimpleTimeZone class provides support for a Gregorian calendar. 

How can a subclass call a method or a constructor defined in a superclass? 

Use the following syntax: super.myMethod(); To call a constructor of the superclass, just write super(); in the first line of the subclass's constructor. 

What is the Properties class? 

The properties class is a subclass of Hashtable that can be read from or written to a stream. It also provides the capability to specify a set of default values to be used. 

What is the purpose of the Runtime class? 

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

What is the purpose of the System class?

The purpose of the System class is to provide access to system resources. 

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

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

What is the Locale class? 

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

What is an abstract method? 

An abstract method is a method whose implementation is deferred to a subclass. Or, a method that has no implementation. 

What is the difference between interface and abstract class? 

interface contains methods that must be abstract; abstract class may contain concrete methods. interface contains variables that must be static and final; abstract class may contain non-final and final variables. members in an interface are public by default, abstract class may contain non-public members. interface is used to "implements"; whereas abstract class is used to "extends". interface can be used to achieve multiple inheritance; abstract class can be used as a single inheritance. interface can "extends" another interface, abstract class can "extends" another class and "implements" multiple interfaces. interface is absolutely abstract; abstract class can be invoked if a main() exists. interface is more flexible than abstract class because one class can only "extends" one super class, but "implements" multiple interfaces. If given a choice, use interface instead of abstract class. 

What is a static method? 

A static method is a method that belongs to the class rather than any object of the class and doesn't apply to an object or even require that any objects of the class have been instantiated. 

What is a protected method? 

A protected method is a method that can be accessed by any method in its package and inherited by any subclass of its class.

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