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Ans. Though It's often confused with each other, Object Creation ( Instantiation ) and Initialization ( Construction ) are different things in Java. Construction follows object creation.
Object Creation is the process to create the object in memory and returning its handler. Java provides New keyword for object creation.
Initialization is the process of setting the initial / default values to the members. Constructor is used for this purpose. If we don't provide any constructor, Java provides one default implementation to set the default values according to the member data types.
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Ans. An interface without any method declaration is called as marker interface. there are 3 in-built interfaces in JVM i.e. serializable, clonable, remote
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Ans. As we only downcast class in the hierarchy, The ClassCastException is thrown to indicate that code has attempted to cast an object to a subclass of which it is not an instance.
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Ans. 1.this is a reference to the current object in which this keyword is used whereas super is a reference used to access members specific to the parent Class.
2.this is primarily used for accessing member variables if local variables have same name, for constructor chaining and for passing itself to some method whereas super is primarily used to initialize base class members within derived class constructor.
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Ans. Both belong to the class as a whole and not to the individual objects. Static methods are explicitly called for execution whereas Static block gets executed when the Class gets loaded by the JVM.
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Ans. A child object constructor always first needs to construct its parent. In Java it is done via an implicit call to the no-args constructor as the first statement
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Ans. At the beginning of an object's life, the Java virtual machine (JVM) allocates memory on the heap to accommodate the object's instance variables. When that memory is first allocated, however, the data it contains is unpredictable. If the memory were used as is, the behavior of the object would also be unpredictable. To guard against such a scenario, Java makes certain that memory is initialized, at least to predictable default values before it is used by any code.
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Constructor provided by Java if no constructor is declared
Constructor with empty body
All of the above
Default Constructor is provided by Java ...
To Reserve Memory
To provide at least one instance method
To Make it look good
To initialize the object state
Q51. Will the static block be executed in the following code ? Why ?
class Test { static { System.out.println("Why I am not executing "); } public static final int param=20; }
public class Demo { public static void main(String[] args) { System.out.println(Test.param); } }
Ans. No the static block won't get executed as the referenced variable in the Test class is final. Compiler replaces the content of the final variable within Demo.main method and hence actually no reference to Test class is made.
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public static void main(String[] args){
System.out.println("Main Method");
new BuggyBread();
}
}
Instance Initialization Block
Constructor
Static Block
Main Method
Static Block
Instance Initialization Block
Constructor
Main Method
Main Method
Static Block
Instance Initialization Block
Constructor
Static Block
Main Method
Instance Initialization Block
Constructor
Q52. Which of the following is false about Constructors ?
a. Constructor can be overloaded b. A no argument constructor is provided by the compiler if we declare only constructors with arguments. c. Constructors shouldn't have any return types , not even void. d. If super is not explicitly called, still super() is intrinsically added by the compiler.
Ans. Only declaring variables as final makes them immutable. Making objects final means that the object handler cannot be used to target some other object but the object is still mutable.
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Static methods belong to the class and not the objects. They belong to the class and hence doesn't fit properly for the polymorphic behavior.
A static method is not associated with any instance of a class so the concept of overriding for runtime polymorphism using static methods is not applicable.
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Which of the following is a Marker Interface ?
