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What is a constructoris it mandatory to use constructor in a class?
You always should define default constructor for your class. You must also define a copy constructor for your class if there are any pointers in the class. While it is not mandatory, failure to provide a default constructor can result in bad behavior, and failure to provide a copy constructor when you have pointers in the class will result in bad behavior. For example, without a default constructor, the compiler will not fully initialize the attributes of the class. It will initialize the virtual function table, and call base class constructors, but that is all - the attributes could be random garbage. For another example, without a copy constructor, the compiler will generate one that simply makes a bit wise copy of the attributes. If these attributes contain pointers, then you have two pointers to the same object, not necessarily a good thing, especially if one of them get "deleted".
Can you initialize an object without constructor in java?
No. if you wish to create an object that you plan on using in a java program then the answer is NO. You cannot initialize an object of a Java class without calling the constructor.
Can a constructor be defined within a method in java?
No.
Why not sending arefrence to copy constructor will cause an infinite loop?
A copy constructor gets called any time an object needs to be copied. Unlike in some of the newer languages like Java, you can chose to pass objects either by reference or by value. When you pass by reference, only the address of the function is copied. However, if you pass by value, the whole object must be copied. In order to copy the object, the copy constructor will get called. If the copy constructor's parameter is not a reference, then the object will get passed by value. When the object gets passed by value, it needs to get copied so it will call the same copy constructor. Because the object is still being passed by value it'll call itself again to create a copy of itself. The copy constructor will continue to call itself until the stack overflows.
What is a constructor and its mandatory to use constructor in a class?
A constructor is a method that is invoked when an object is created. As to being mandatory, that really depends on the programming language; in the case of Java, each class must have a constructor, however, in many cases Java will automatically provide a default constructor, so you don't really need to program it.
