What keyword is used to extend a class in Java?
- extends
- implements
- inherits
- subclass
In Java, the extends keyword is used to indicate inheritance and extend a class. When a class extends another class, it inherits all the members (fields and methods) of the parent class, allowing you to create a subclass that inherits and extends the functionality of the superclass.
The method ________ of FileOutputStream class is used to write a specific byte of data to a file output stream.
- append
- write
- writeByte
- writeData
The write method of the FileOutputStream class is used to write a specific byte of data to a file output stream. You can use this method to write individual bytes or byte arrays to a file.
What is the default constructor in Java?
- A constructor provided by Java for every class
- A constructor with a single parameter
- A constructor with default values
- A constructor with no parameters
In Java, the default constructor is a constructor provided by Java for every class that doesn't explicitly define its own constructor. It takes no parameters and initializes instance variables to their default values. The other options do not accurately describe the default constructor in Java.
Imagine a scenario where you are developing a library, and you want to restrict the usage of some specific methods to the external world but allow them to be used inside the package. How would you implement this using access modifiers?
- package-private
- private
- protected
- public
To restrict the usage of certain methods to the external world while allowing them to be used within the package, you would use the package-private access modifier. This is achieved by not specifying any access modifier (default) before the method declaration. Public methods are accessible from anywhere, private methods are restricted to the class, and protected methods allow access within the package and subclasses.
Why does Java not support operator overloading?
- Because it's not feasible to implement
- To avoid ambiguity in code
- To promote method overloading instead
- To simplify the language and reduce complexity
Java does not support operator overloading primarily to simplify the language and reduce complexity. Operator overloading can lead to ambiguity in code, making it harder to read and maintain. Instead, Java encourages method overloading as a way to achieve similar functionality.
________ collection classes store objects, whereas ________ collection classes store primitive data types.
- ArrayList / LinkedList
- HashMap / HashSet
- Vector / Hashtable
- Wrapper / Primitive
Wrapper collection classes (such as ArrayList) store objects, while Primitive collection classes (such as ArrayList) store primitive data types directly. The wrapper classes allow primitive data types to be used in collections that require objects.
What will happen if you try to assign a value larger than the maximum value of the byte data type to a byte variable?
- A compilation error will occur because it's not possible to assign a larger value.
- An exception will be thrown at runtime.
- The byte variable will automatically promote to a larger data type to accommodate the value.
- The value will be truncated to fit within the range of the byte data type.
In Java, if you try to assign a value larger than the maximum value (127) of the byte data type to a byte variable, the value will be truncated, and the least significant bits will be retained. This is known as "overflow." The other options do not accurately describe the behavior of byte variables.
How can you efficiently represent sparse matrices using multi-dimensional arrays in Java?
- Use a hashmap to store non-empty elements with keys representing row and column indices for fast retrieval.
- Use a linked list of linked lists to represent rows and columns, only storing non-empty elements.
- Use a one-dimensional array to store non-empty values along with their row and column indices for efficient access.
- Use a two-dimensional array with default values set to null or another sentinel value to represent empty elements.
To efficiently represent sparse matrices in Java, you can use a one-dimensional array to store non-empty values along with their row and column indices. This approach minimizes memory usage and provides fast access to non-empty elements. The other options do not efficiently address the issue of sparse matrices.
Which of the following data types can store a null value in Java?
- Integer
- String
- double
- int
In Java, only reference data types (objects) can store a null value. Among the given options, String is a reference data type that can store null. The other options are primitive data types and cannot hold null values.
What are the challenges of implementing operator overloading in Java?
- Java does not support operator overloading, so there are no challenges to address.
- The challenge is defining custom operators, which may not be intuitive to developers familiar with Java's standard operators.
- The challenge is the risk of causing performance issues due to overloaded operators.
- The main challenge is ambiguity, as overloading operators can lead to confusion and unintended behavior.
The main challenge of implementing operator overloading in Java is ambiguity. Operator overloading can lead to confusion and unintended behavior, making the code less readable and maintainable. Since Java doesn't support operator overloading for user-defined classes, developers are encouraged to use meaningful method names instead.