Choose Correct Answer Core Java

The toString() method of the CharArrayWriter class copies and converts the output buffer to a String object. This method returns a string that contains the characters in the buffer.

The correct answer is "Null". When the readLine() function has reached the end of the file, it returns a null value. This indicates that there are no more lines to be read from the file.

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The Test class has two constructors - one that takes an integer parameter and another that takes two integer parameters. Option 1 is not a legitimate call because it does not match any of the available constructors. Option 2 is a legitimate call because it matches the constructor that takes a single integer parameter. Option 3 is also a legitimate call because it matches the constructor that takes two integer parameters. Therefore, the correct answer is 2,3.

The correct answer is 1,3. In option 1, int $x; is a valid declaration because it starts with a letter or an underscore. In option 2, int 123; is not a valid declaration because it starts with a number. In option 3, int _123; is a valid declaration because it starts with an underscore. Therefore, options 1 and 3 are the valid declarations.

A reference variable's type determines the methods that can be invoked on the object the variable is referencing. This is because the type of the reference variable determines the available methods and properties of the object it refers to.

A reference is a variable, so it can be reassigned to other objects (unless the reference is declared final). This means that the reference variable can be pointed to a different object at any time during the program execution, allowing for flexibility in manipulating and accessing different objects.

The correct answer is FileInputStream, Reader. This is because both FileInputStream and Reader are abstract classes defined in the java.io package and are used for file-handling. Abstract classes cannot be instantiated and are meant to be extended by subclasses.

The File class in Java is used to access files and directories on the local file system, so statement 4 is true. File objects can be used to access the files in the current working directory, making statement 2 true. File objects can also be garbage collected, which means they can be automatically cleaned up by the Java garbage collector, making statement 5 true. Therefore, the correct answer is 2, 4, 5.

Filters are supported by the InputStream/OutputStream class hierarchy but not by the Reader/Writer class hierarchy. This means that filters can be applied to input streams and output streams, but not to reader and writer objects. Filters are used to alter data that is read from one stream and written to another.

An anonymous inner class in Java can implement at most one interface, as stated in option 1. This means that it can only provide the implementation for the methods defined in a single interface. However, an anonymous inner class can also extend a parent class other than Object, as mentioned in option 3. This allows the anonymous inner class to inherit the properties and methods of the parent class. Therefore, the correct answer is 1,3.

The correct answer is 3. The notify() method is not defined in class java.lang.Thread. The notify() method is actually defined in class java.lang.Object. The notify() method is used to wake up a single thread that is waiting on the object's monitor.

A static nested class is a nested class that is declared with the static keyword. This means that it can be accessed without creating an instance of the enclosing class. Therefore, statement 1 is false. However, since it is a nested class, it does have access to both static and non-static members of the enclosing class. Therefore, statement 2 is false. Finally, there is no requirement for the variables and methods of a static nested class to be static. Therefore, statement 3 is true.

When a stack variable goes out of scope, it means that it is no longer accessible or in use by the program. At this point, the variable becomes eligible for garbage collection because it is no longer needed. This is true because stack variables are automatically deallocated when they go out of scope, while heap variables require manual deallocation. Therefore, statement 2 is true.

If we insert the code from option 1 at line 6, it will compile because it is a valid method declaration that accepts a variable number of arguments of type int.
If we insert the code from option 2 at line 6, it will also compile because it is a valid method declaration that accepts an array of type int.
If we insert the code from option 3 at line 6, it will compile because it is a valid method declaration that accepts an int followed by a variable number of arguments of type int. Therefore, options 1, 2, and 3 can all be inserted independently at line 6 and will compile.

The correct answer is 3 because a method with a private access modifier can only be accessed within the same class and cannot be overridden in a subclass. Therefore, option 3, which has a private access modifier, can override the method void xyz(float f).

After executing the line of code "int []x=new int[25];", x[24] is not 0 or undefined. Since arrays in Java are zero-indexed, the last element of the array would be at index 24. However, this line of code only initializes the array and does not assign any values to its elements. Therefore, the value of x[24] would be the default value for an int, which is 0. However, x[24] is not undefined because it has been allocated memory and has a default value of 0. Similarly, x[25] is not 0 because it is out of bounds of the array. Therefore, the correct answer is "None of the above."

The correct answer is "new FileInputStream("file.name")". This option is the most suitable for reading in a large text file because it directly reads the file as a stream of bytes, without any additional buffering or conversions. The other options involve additional layers of buffering or conversion, which may not be necessary and could potentially slow down the reading process for a large file.

The code creates a new thread and starts it. Then, it prints "X" and calls the wait() method on the thread object, causing the main thread to wait for 10 seconds. However, since the wait() method must be called within a synchronized block, an exception is thrown at runtime. Therefore, the correct answer is that an exception is thrown at runtime.

The instanceOf operator in Java is used to check whether an object is an instance of a particular class or interface. On the left-hand side of the instanceOf operator, we can have a reference to an object (option 1) or an interface (option 3). A reference can be used to check if an object is an instance of a specific class or interface, while an interface can be used to check if an object implements a specific interface. Therefore, options 1 and 3 are correct.

The argument list must exactly match that of the overridden method is not applicable for overriding. The return type can be of any type and the access level can be more restrictive than the overridden method are the applicable rules for overriding.

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The correct answer is 2,4,5. The methods available(), flush(), and write() are not methods of the InputStream class. The available() method is used to return the number of bytes that can be read from the input stream without blocking. The flush() method is used to flush the output stream and write() method is used to write bytes to the output stream.

The correct answer is 3. The explanation for this answer is that all three classes (String, StringBuilder, and StringBuffer) have a length() method, which allows you to retrieve the length of the string. Additionally, the value of an instance of any of these three types can be modified through various methods in the API. However, only objects of type StringBuffer are thread-safe, meaning they can be safely used in a multi-threaded environment without any issues.

The PipedOutputStream and ObjectInputStream classes enable objects and values of primitive types to be written to and read from streams. The PipedOutputStream class is used to write data to a pipe, while the ObjectInputStream class is used to read serialized objects from an input stream. Together, these classes provide the functionality to transfer objects and primitive values between different parts of a program using streams.

Constructors are special methods in a class that are used to initialize objects of that class. They cannot have a return type, therefore statement 3 is not true. Additionally, the constructor name should indeed match the name of the class, so statement 2 is also not true. However, constructors can use any access modifier, including private, so statement 1 is true. Therefore, the correct answer is 1.