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This week Making Java Groovy is the featured book at JavaRanch, where I've been a member for many years. JavaRanch is yet another of Kathy Sierra's (and ... Stuff I've learned recently... | ||||||||
Wednesday, September 18
Top Java News- September 18 ,2013
Tuesday, September 17
CQ5 Author or Publisher instance is down due to OutOfMemoryError.
Overview
OutOfMemoryError can occur any time in heap due to insufficient heap memory being available for new Java objects creation. CQ Author/Publisher will eventually crash due to OutOfMemoryError and would need to be restarted.
Issue
CQ5 Author or Publisher instance is down due to OutOfMemoryError.
Resolution
1.
2. Access all publisher and author instances and note which all instances are not responding.
3. For all instances not responding Access CRX error logs Note down which all instances are throwing OutOfMemoryError. In error log OutOfMemoryError can be searched by searching file content for string ”OutOfMemoryError”
4. For every publisher instance throwing OutOfMemoryError follow the below steps:
5. Execute Datastore Garbage Collection operation in configuration repository. To execute this operation visit http://:/system/console/memoryusage for the publisher instance and click on runDataStoeGarbageCollection operation as shown below.
6. This should free up some memory.
7. Stop the server by executing
8. Start the server by executing
9. Access the publisher instances and note which all publishers are not responding.
10. If all publishers instances are responding well issue is resolved.
Interface Segregation Principle(ISP) - Java design principals , OOPS design principals ,Object oriented design principals , How to design interface in java
Interface Segregation Principle stats that, a client should not implement an interface, if it doesn't use that.
What exaclt does that mean ?
Let's understand this
Consider there is one interface Travel
Travel has two methods
travelbyBus()
travelByTrain()
Now there is one class Passenger . Passenger will always travel by bus .
if Passenger class implements Travel interface
Passenger implements Passenger {
travelbyBus(){
}
travelByTrain(){
}
}
It is forced to implement both the methods travelByBus() and travelByTrain() , thought Passenger has nothing to do with travelByTrain().
Now lets read the principal again
Interface Segregation Principle stats that, a client should not implement an interface, if it doesn't use that.
Client Passenger should not be forced to implement travelByTrain() method as it never needs it.
Here comes the Interface designing best practice .
An interface design should be very thoughtful. It should always take in consideration all its possible clients and should always make interface design client friendly.
So could that be achieved?
Instead of creating one interface for both methods , two separate interfaces could be designed
like :
BusTravel{
travelByBus();
}
TrainTravel{
travelByTrain();
}
Passenger class can implement BusTravel interface and will not be forced to implement anymore method.
Thus Interface Segregation Principle(ISP) basically recommend to design the interfaces taking in consideration holistic ststem and all poosible clients.
Monday, September 16
Liskov Substitution Principle (LSP) : Design Principal , Java Design Principal
Liskov Substitution Principle (LSP)
According to Liskov Substitution Principle, methods or functions which uses super class type must be able to work with object of sub class without any issue".
Let us understand this with an example
Public class Cat extends Animal {
}
public class Animal{
}
Public class TestLSP{
public void execute(Animal animal){
}
public void executor(){
Animal animal =new Animal();
execute(animal);
Cat cat = new Cat();
execute(cat);
}
So we are able to call execute method from executor method by passing Animal class instance as well as Cat class instance .
Cat class extends Animal So is subclass to Animal class.
Thus Animal class parameter expected in executor method works well with Animal as well as subtype Cat type of instance . that's what LSP says.
According to Liskov Substitution Principle, methods or functions which uses super class type must be able to work with object of sub class without any issue".
Let us understand this with an example
Public class Cat extends Animal {
}
public class Animal{
}
Public class TestLSP{
public void execute(Animal animal){
}
public void executor(){
Animal animal =new Animal();
execute(animal);
Cat cat = new Cat();
execute(cat);
}
So we are able to call execute method from executor method by passing Animal class instance as well as Cat class instance .
Cat class extends Animal So is subclass to Animal class.
Thus Animal class parameter expected in executor method works well with Animal as well as subtype Cat type of instance . that's what LSP says.
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