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In C++, it is possible to have uninitialized primitive objects. Java enforces default initialization. In C++, it is possible to have an allocated object to which there is no valid reference. Such an unreachable object cannot be destroyed (deallocated), and results in a memory leak. In contrast, in Java an object will not be deallocated by the ...
When an array of objects is declared, e.g. MyClass x[10];; or allocated dynamically, e.g. new MyClass [10]. The default constructor of MyClass is used to initialize all the elements. When a derived class constructor does not explicitly call the base class constructor in its initializer list, the default constructor for the base class is called.
Java constructors perform the following tasks in the following order: Call the default constructor of the superclass if no constructor is defined. Initialize member variables to the specified values. Executes the body of the constructor. Java permit users to call one constructor in another constructor using this() keyword.
The latter list is sometimes called the "initializer list" or "initialization list" (although the term "initializer list" is formally reserved for initialization of class/struct members in C++; see below). A declaration which creates a data object, instead of merely describing its existence, is commonly called a definition.
Java does not have uninitialized variables. Fields of classes and objects that do not have an explicit initializer and elements of arrays are automatically initialized with the default value for their type (false for boolean, 0 for all numerical types, null for all reference types). [4]
Finally, the constructor body is executed. This ensures proper order of initialization, i.e. the fields of a base class finish initialization before initialization of the fields of an object class begins. There are two main potential traps in Java's object initialization. First, variable initializers are expressions that can contain method calls.
There are valid forms of the pattern, including the use of the volatile keyword in Java and explicit memory barriers in C++. [4] The pattern is typically used to reduce locking overhead when implementing "lazy initialization" in a multi-threaded environment, especially as part of the Singleton pattern. Lazy initialization avoids initializing a ...
[5] new and delete were, in fact, introduced in the first version of C++ (then called "C with Classes") to avoid the necessity of manual object initialization. [ 4 ] In contrast to the C routines, which allow growing or shrinking an allocated array with realloc , it is not possible to change the size of a memory buffer allocated by new[] .