What are the Object and Class classes used for?
The Object class is the highest-level class in the Java class hierarchy. The Class class is used to represent the classes and interfaces that are loaded by a Java program.
What is Serialization and deserialization ?
Serialization is the process of writing the state of an object to a byte stream. Deserialization is the process of restoring these objects.
Explain the usage of Java packages.
This is a way to organize files when a project consists of multiple modules. It also helps resolve naming conflicts when different packages have classes with the same names. Packages access level also allows you to protect data from being used by the non-authorized classes.
Does the code in finally block get executed if there is an exception and a return statement in a catch block?
If an exception occurs and there is a return statement in catch block, the finally block is still executed. The finally block will not be executed when the System.exit(1) statement is executed earlier or the system shut down earlier or the memory is used up earlier before the thread goes to finally block.
Is Java a super set of JavaScript?
No. They are completely different. Some syntax may be similar.
What is a Container in a GUI?
A Container contains and arranges other components (including other containers) through the use of layout managers, which use specific layout policies to determine where components should go as a function of the size of the container.
How the object oriented approach helps us keep complexity of software development under control?
We can discuss such issue from the following aspects:
Objects allow procedures to be encapsulated with their data to reduce potential interference.
Inheritance allows well-tested procedures to be reused and enables changes to make once and have effect in all relevant places.
The well-defined separations of interface and implementation allow constraints to be imposed on inheriting classes while still allowing the flexibility of overriding and overloading.
What is polymorphism?
Polymorphism means "having many forms". It allows methods (may be variables) to be written that needn't be concerned about the specifics of the objects they will be applied to. That is, the method can be specified at a higher level of abstraction and can be counted on to work even on objects of un-conceived classes.
What is design by contract?
The design by contract specifies the obligations of a method to any other methods that may use its services and also theirs to it. For example, the preconditions specify what the method required to be true when the method is called. Hence making sure that preconditions are. Similarly, postconditions specify what must be true when the method is finished, thus the called method has the responsibility of satisfying the post conditions.
In Java, the exception handling facilities support the use of design by contract, especially in the case of checked exceptions. The assert keyword can be used to make such contracts.
What are use cases?
A use case describes a situation that a program might encounter and what behavior the program should exhibit in that circumstance. It is part of the analysis of a program. The collection of use cases should, ideally, anticipate all the standard circumstances and many of the extraordinary circumstances possible so that the program will be robust.
What is scalability and performance?
Performance is a measure of "how fast can you perform this task." and scalability describes how an application behaves as its workload and available computing resources increase.
What is the benefit of subclass?
Generally: The sub class inherits all the public methods and the implementation.
The sub class inherits all the protected methods and their implementation.
The sub class inherits all the default(non-access modifier) methods and their implementation.
The sub class also inherits all the public, protected and default member variables from the super class.
The constructors are not part of this inheritance model.
How to add menushortcut to menu item?
If you have a button instance called aboutButton, you may add menu short cut by calling aboutButton.setMnemonic('A'), so the user may be able to use Alt+A to click the button.
In System.out.println(),what is System,out and println,pls explain?
System is a predefined final class,out is a PrintStream object acting as a field member and println is a built-in overloaded method in the out object.
Can you write a Java class that could be used both as an applet as well as an application?
A. Yes. Add a main() method to the applet.
Can you make an instance of an abstract class? For example - java.util.Calender is an abstract class with a method getInstance() which returns an instance of the Calender class.
No! You cannot make an instance of an abstract class. An abstract class has to be sub-classed. If you have an abstract class and you want to use a method which has been implemented, you may need to subclass that abstract class, instantiate your subclass and then call that method.
What is the output of x > y? a:b = p*q when x=1,y=2,p=3,q=4?
When this kind of question has been asked, find the problems you think is necessary to ask back before you give an answer. Ask if variables a and b have been declared or initialized. If the answer is yes. You can say that the syntax is wrong. If the statement is rewritten as: x
What is the difference between Swing and AWT components?
AWT components are heavy-weight, whereas Swing components are lightweight. Heavy weight components depend on the local windowing toolkit. For example, java.awt.Button is a heavy weight component, when it is running on the Java platform for Unix platform, it maps to a real Motif button.
Why Java does not support pointers?
Because pointers are unsafe. Java uses reference types to hide pointers and programmers feel easier to deal with reference types without pointers. This is why Java and C-sharp shine.
Parsers? DOM vs SAX parser
Parsers are fundamental xml components, a bridge between XML documents and applications that process that XML. The parser is responsible for handling xml syntax, checking the contents of the document against constraints established in a DTD or Schema.
DOM
1. Tree of nodes
2. Memory: Occupies more memory, preffered for small XML documents
3. Slower at runtime
4. Stored as objects
5. Programmatically easy
6. Ease of navigation
SAX
1. Sequence of events
2. Doesn't use any memory preferred for large documents
3. Faster at runtime
4. Objects are to be created
5. Need to write code for creating objects
6. Backward navigation is not possible as it sequentially processes the document
Can you declare a class as private?
Yes, we can declare a private class as an inner class. For example,
class MyPrivate {
private static class MyKey {
String key = "12345";
}
public static void main(String[] args) {
System.out.println(new MyKey().key);//prints 12345
}
}
What is the difference between shallow copy and deep copy?
Shallow copy shares the same reference with the original object like cloning, whereas the deep copy get a duplicate instance of the original object. If the shallow copy has been changed, the original object will be reflected and vice versa.
Can one create a method which gets a String and modifies it?
No. In Java, Strings are constant or immutable; their values cannot be changed after they are created, but they can be shared. Once you change a string, you actually create a new object. For example:
String s = "abc"; //create a new String object representing "abc"
s = s.toUpperCase(); //create another object representing "ABC"
Why is multiple inheritance not possible in Java?
It depends on how you understand "inheritance". Java can only "extends" one super class, but can "implements" many interfaces; that doesn't mean the multiple inheritance is not possible. You may use interfaces to make inheritance work for you. Or you may need to work around. For example, if you cannot get a feature from a class because your class has a super class already, you may get that class's feature by declaring it as a member field or getting an instance of that class. So the answer is that multiple inheritance in Java is possible.
What's the difference between constructors and other methods?
Constructors must have the same name as the class and can not return a value. They are only called once while regular methods could be called many times.
Core Java (Part VI) 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.
What restrictions are placed on method overriding?
Overridden methods must have the same name, argument list, and return type. The overriding method may not limit the access of the method it overrides. The overriding method may not throw any exceptions that may not be thrown by the overridden method.
What is casting?
There are two types of casting, casting between primitive numeric types and casting between object references. Casting between numeric types is used to convert larger values, such as double values, to smaller values, such as byte values. Casting between object references is used to refer to an object by a compatible class, interface, or array type reference.
Explain the usage of the keyword transient?
This keyword indicates that the value of this member variable does not have to be serialized with the object. When the class will be de-serialized, this variable will be initialized with a default value of its data type (i.e. zero for integers).
What class allows you to read objects directly from a stream?
The ObjectInputStream class supports the reading of objects from input streams.
How are this() and super() used with constructors?
this() is used to invoke a constructor of the same class. super() is used to invoke a superclass constructor.
How is it possible for two String objects with identical values not to be equal under the == operator? How are this() and super() used with constructors?
The == operator compares two objects to determine if they are the same objects in memory. It is possible for two String objects to have the same value, but located in different areas of memory. What is an IO filter?
An IO filter is an object that reads from one stream and writes to another, usually altering the data in some way as it is passed from one stream to another.
What is the Set interface?
The Set interface provides methods for accessing the elements of a finite mathematical set. Sets do not allow duplicate elements.
How can you force garbage collection?
You can't force GC, but could request it by calling System.gc(). JVM does not guarantee that GC will be started immediately.
What is the purpose of the enableEvents() method?
The enableEvents() method is used to enable an event for a particular object. Normally, an event is enabled when a listener is added to an object for a particular event. The enableEvents() method is used by objects that handle events by overriding their event-dispatch methods.
What is the difference between the File and RandomAccessFile classes?
The File class encapsulates the files and directories of the local file system. The RandomAccessFile class provides the methods needed to directly access data contained in any part of a file.
What interface must an object implement before it can be written to a stream as an object?
An object must implement the Serializable or Externalizable interface before it can be written to a stream as an object.
What is the ResourceBundle class?
The ResourceBundle class is used to store locale-specific resources that can be loaded by a program to tailor the program's appearance to the particular locale in which it is being run.
How do you know if an explicit object casting is needed?
If you assign a superclass object to a variable of a subclass's data type, you need to do explicit casting. For example:
Object a; Customer b; b = (Customer) a;
When you assign a subclass to a variable having a supeclass type, the casting is performed automatically.
What is a Java package and how is it used?
A Java package is a naming context for classes and interfaces. A package is used to create a separate name space for groups of classes and interfaces. Packages are also used to organize related classes and interfaces into a single API unit and to control accessibility to these classes and interfaces.
How do you restrict a user to cut and paste from the html page?
Using Servlet or client side scripts to lock keyboard keys. It is one of solutions.
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.
What restrictions are placed on method overriding?
Overridden methods must have the same name, argument list, and return type. The overriding method may not limit the access of the method it overrides. The overriding method may not throw any exceptions that may not be thrown by the overridden method.
What is casting?
There are two types of casting, casting between primitive numeric types and casting between object references. Casting between numeric types is used to convert larger values, such as double values, to smaller values, such as byte values. Casting between object references is used to refer to an object by a compatible class, interface, or array type reference.
Explain the usage of the keyword transient?
This keyword indicates that the value of this member variable does not have to be serialized with the object. When the class will be de-serialized, this variable will be initialized with a default value of its data type (i.e. zero for integers).
What class allows you to read objects directly from a stream?
The ObjectInputStream class supports the reading of objects from input streams.
How are this() and super() used with constructors?
this() is used to invoke a constructor of the same class. super() is used to invoke a superclass constructor.
How is it possible for two String objects with identical values not to be equal under the == operator? How are this() and super() used with constructors?
The == operator compares two objects to determine if they are the same objects in memory. It is possible for two String objects to have the same value, but located in different areas of memory. What is an IO filter?
An IO filter is an object that reads from one stream and writes to another, usually altering the data in some way as it is passed from one stream to another.
What is the Set interface?
The Set interface provides methods for accessing the elements of a finite mathematical set. Sets do not allow duplicate elements.
How can you force garbage collection?
You can't force GC, but could request it by calling System.gc(). JVM does not guarantee that GC will be started immediately.
What is the purpose of the enableEvents() method?
The enableEvents() method is used to enable an event for a particular object. Normally, an event is enabled when a listener is added to an object for a particular event. The enableEvents() method is used by objects that handle events by overriding their event-dispatch methods.
What is the difference between the File and RandomAccessFile classes?
The File class encapsulates the files and directories of the local file system. The RandomAccessFile class provides the methods needed to directly access data contained in any part of a file.
What interface must an object implement before it can be written to a stream as an object?
An object must implement the Serializable or Externalizable interface before it can be written to a stream as an object.
What is the ResourceBundle class?
The ResourceBundle class is used to store locale-specific resources that can be loaded by a program to tailor the program's appearance to the particular locale in which it is being run.
How do you know if an explicit object casting is needed?
If you assign a superclass object to a variable of a subclass's data type, you need to do explicit casting. For example:
Object a; Customer b; b = (Customer) a;
When you assign a subclass to a variable having a supeclass type, the casting is performed automatically.
What is a Java package and how is it used?
A Java package is a naming context for classes and interfaces. A package is used to create a separate name space for groups of classes and interfaces. Packages are also used to organize related classes and interfaces into a single API unit and to control accessibility to these classes and interfaces.
How do you restrict a user to cut and paste from the html page?
Using Servlet or client side scripts to lock keyboard keys. It is one of solutions.
Subscribe to:
Posts (Atom)