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Autoboxing and Unboxing in Java

In java, we often need to convert primitive types to their object(boxed wrappers) counterparts or vice versa. Unfortunately, doing these conversions all the time is tedious and make code verbose. For this reason, Java 1.5 introduced two concepts, autoboxing and unboxing, that automate these conversions.

Autoboxing: It is the process of converting primitives to their corresponding object type automatically.

Unboxing:It is the process of converting object types to their corresponding primitives automatically.

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Software

Understanding equals and hashcode in Java

In Java, Object class has two identity methods called equals and hashcode. We usually override them in our classes to achieve equality. Understanding the underlying mechanism of equals and hashcode can be crucial in some cases. Let’s take a brief look at what they are used for.

  • equals : compares two objects in order to determine if they are equal or not. If you do not override this method or no parent class overrides it, equals method acts like == operator by default. (Beware that == operator compares object references not values.)
  • hashcode: provides and an int value which is derived from the memory address of the object. If two objects occupy same memory address they have same hashcode by default.

If you leave equals and hashcode methods as it is, one can conclude that whenever equals is true for two object, their hashcode value must be same.

So in order to not to break this rule, if you override one of these methods, you must override both.

We have equals, why do we need hashcode ?

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Software

Argument passing in Java

Argument passing in Java is simple but sometimes confusing. Let’s go over some concepts briefly before diving into it.

If you come from a C/C++ programming background, you’ve probably heard of the “Call By Value” and “Call By Reference” argument passing concepts.

Briefly,

  • Call by Value : A copy of the object instance is passed to called method. Any modifications made on the object inside the method will not be reflected back to the original object.
  • Call by Reference : A reference to  the original object is passed to called function. This reference may be thought as an alias for the original object and any modification done on the alias object inside the method actually done on the original object.

In this sense what about JAVA?