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Welcome you at the JAVA BOOTS.

Its a place where u find,discuss,share common problems,coding strategies, design principles etc in java and related technologies. I keep sharing my learnings here. Hope it will be helpful to all.

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When to use getClass() and instanceOf in Java

getClass() only gives equality if two objects belong to same class whereas instanceOf works for subtype also. If two objects of different classes are checked for equal, then we use instanceOf . But once you use instanceOf at some level in the class hierarchy everything below it must use instanceOf or you will violatate the symmetry clause of equals contract.  e.g. any list can be equal to any list as long they have same elements iun the same order. So any List implementation equals() method must do instanceOf and not getclass() and then compare. On the other hand, it only make sense for na instance of class X to be equal to another instance of class X ( and not any subclass ) , then use getClass().
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Fix double check locking in Java 5

We can fix the double check locking  using volatile keyword. In Java 5, the JRE system will not allow a write of volatile to be reordered i.e read and write of volatile cannot be reordered w.r.t any previous read and write. So the volatile always gives the latest value. class Foo{ private volatile Helper helper=null; public Helper getHelper(){ if(helper=null){ synchronized(this){ if(helper=null) helper=new Helper(); } } return helper; } }
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Where to declare Constants in Java

Its been an topic of debate where should constants be declared. Let look at approaches :- Declared in an Interface. Declared in a Class. Enums Going through google, i found number of explanation for both of these. Each have their pros and cons. I'll try to summarise and share my thoughts on it. Lets start with interface . In Java, Interfaces are used as abstract type, that contain method signatures, constants and nested types as  according to Oracle . We can use interfaces to defined a contract or for communication  as explained in my previous article . If we define constants here, we can have the following consequences:- We cannot stop a class to not implement an interface.So a Global constant interface can be used for subtype which is not advisable. We cannot give define constants depend on certain state condition. All the constants would stay in memory all the time. Although, we can define constants in interfaces, we have the above constraints. Lets...
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