hashCode() method in java

public int hashCode() : Returns a hash code value for the object.

- As much as is reasonably practical, the hashCode method defined by class Object does return distinct integers for distinct objects.
- If two object are equal a/c to the equals() method, then calling hashCode() on those object must produce the same hash value.
- It's not mandatory that if hash values of two object are equal, then the two objects should be equal.

It's generally said,

Adapter design pattern in Java with example

This is a structural design pattern. A Wrapper class, i.e., Adatper class is used to convert requests from it to Adaptee class.

The Adapter pattern converts the interface of a class into another interface the client expect. Adapter lets classes work together that couldn't otherwise because of incompatible interfaces.

Two forms of Adapter pattern:

1) class adapter (uses inheritace)

2) object adapter (uses composition)

object adapter 

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object adapter design pattern

 

A simple example

Comparator and Comparable example in Java

java.lang.Comparable
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int compareTo(Object o) : This method compares 'this' object with 'o' object

if the int value is
positive - 'this' object is greater than 'o' object
zero - 'this' object is equals with 'o' object
negative - 'this' object is less than 'o' object

java.util.Comparator
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int compare(Object o1,Object o2) : This method compares o1 and o2 objects.

if the int values is
positive - o1 is greater than o2
zero - o1 equals o2
negative - o1 is less than o2

A simple example

Sandbox model in Java

The Original Sandbox Model 
The original security model provided by the Java platform is known as the sandbox model, which existed in order to provide a very restricted environment in which to run untrusted code obtained from the open network. The essence of the sandbox model is that local code is trusted to have full access to vital system resources (such as the file system) while downloaded remote code (an applet) is not trusted and can access only the limited resources provided inside the sandbox.

Eclipse shortcut keys

Ctrl + D - Delete Row

Alt + Up/Down Arrow - Move the row up/down

Alt + Left/Right Arrow - Switch b/w files you last edited

Ctrl + Shift + O - All the required imports will be done,Unused imports will vanish

Ctrl + 1 - while implementing an interface we'll get error,because inherited methods not  yet implemented.This key acts as quick fix.

Ctrl + Shift + T - Open Type.Search the classes

clone() method in Java

We'll generally create clone, when we want to create local copy of the object and don't want to modify the original object.
Use the clone() method cautiously, or else you can also create a copy constructor alternative to the clone().
This is a protected method in java.lang.Object class.
protected Object clone() CloneNotSupportedException : It creates and returns a copy of this object.

By default shallow copy is applied. If we want extra logic to be impemented then we need to opt for deep copy.
Shallow copy : Just call the super.clone()
Deep copy : We need to implement ourselves.

A simple example

toString() method in Java

This method returns the string representation of the object.
If we try to print the object directly without overriding the toString() method for that calss, then we'll get the output  in the format.

ClassName@HexDecRepresentationOfObject or
getClass().getName() + '@' + Integer.toHexString(hashCode())

By default ArrayList overrides the toString method, so if we print the object of ArrayList it'll nicely print the added objects.

A simple example

ServletContextListener in Java Servlets

ServletContextListener

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We can't very well stuff 'object' into an XML DD. We can do this by Listeners if, we want objects those required by any resource of app.

If we want to run some code before the rest of the app service a client, then we have context init parameters that we can get and use.

Methods in ServletContextListener

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contextInitialized(ServletContextEvent)

contextDestroyed(ServletContextEvent)

A simple example