COBOL and Java Programming Fundamentals

In Java's main(String[] args), args[0] is the first command-line argument passed to the program. Unlike C/C++, Java does not include the program name in the args array. If no arguments are provided, the array is empty and accessing args[0] would throw ArrayIndexOutOfBoundsException.

A concrete class implementing an interface must provide implementations for all interface methods. However, if the implementing class is abstract, it can defer implementation to its subclasses. Option A is too absolute, C is false (abstract classes can implement interfaces), and D is incorrect because B is valid.

Abstract classes can contain both abstract and concrete (non-abstract) methods. This is a key distinction from interfaces. Abstract classes provide partial implementation with abstract methods defining what subclasses must implement, and concrete methods providing shared behavior.

An abstract class in Java cannot be declared as final because abstract classes are designed to be extended by subclasses, whereas final classes explicitly prevent inheritance. These two modifiers are mutually exclusive.

'super' is a reserved keyword in Java, not a method. It is used to access superclass members (super.method() or super.field) or to call a superclass constructor (super() as the first statement in a constructor). It cannot be used as a variable name or for any other purpose.

While Java permits accessing static members through an object reference (obj.staticMethod()), this is misleading and discouraged. Static members belong to the class, not instances. The correct practice is ClassName.staticMethod(). The compiler actually uses the declared type of the reference, not the runtime object.

Java only provides a default no-argument constructor if no other constructor is explicitly defined. Once you define any constructor (with or without arguments), the default constructor is not automatically generated. If you need both parameterized and no-arg constructors, you must explicitly define both.

Private member variables in a superclass are not accessible to subclasses - this is a fundamental principle of encapsulation in object-oriented programming. Only the superclass itself can access its private members. Subclasses can only access public, protected, and package-private (if in same package) members.

Interfaces in Java can extend any number of other interfaces, allowing multiple inheritance of type. This is different from classes which can only extend one class. Interfaces do not 'implement' other interfaces - they extend them. Interface members are implicitly public and can be static (default methods are instance methods). A class can extend only one class due to single inheritance.

The conditional expression in an if statement can indeed contain method calls as long as they return boolean. Assignment expressions like (a = b) are also allowed because assignment returns the assigned value, which for boolean types is boolean. The statement 'if (false) ; else ;' is legal syntax (empty statements). Only boolean-valued expressions can serve as if conditions in Java.

Private methods are not visible to subclasses and therefore cannot be overridden. A subclass can only override public and protected methods. An overriding method cannot declare more checked exceptions than the overridden method. The parameter list must match exactly (same number and types). The return type must be covariant (same type or subtype).

In COBOL, PIC S9(9)V9(9) declares a signed numeric variable with 9 digits before and 9 digits after the decimal point. This occupies 18 bytes in display format (each digit requires one byte, plus one for sign, and V is implicit decimal). The V indicates an implied decimal point position and doesn't occupy storage.

When B is statically linked to C, C's code is embedded in B at link time. If C changes, B must be recompiled and relinked to incorporate the new version. A doesn't need recompilation because it links dynamically to B - it will use the updated B at runtime. Only B needs relinking.

The DELETE statement in COBOL requires the file to be opened in I-O mode. I-O mode allows both reading and writing operations, which is necessary for delete operations. INPUT mode only allows reading, OUTPUT mode only allows writing new records, neither supports deletion of existing records.

START statement is used to position a file at a specific record for sequential processing. When ACCESS MODE is RANDOM, records are accessed directly by key, making sequential positioning operations like START invalid. READ, WRITE, and REWRITE are all valid operations for RANDOM access mode on relative files.

In COBOL, to execute a WRITE statement on a sequential file, the file must be opened in either OUTPUT or EXTEND mode. Opening a file in INPUT mode makes it read-only, which makes WRITE operations invalid.

In a SORT statement with multiple keys, the first key listed is the major (primary) sort key, and subsequent keys are minor (secondary) keys. Here IBM-MAIN is listed before Y2K-MAIN, so it's the major key. Records are sorted first by IBM-MAIN, then within matching IBM-MAIN values, by Y2K-MAIN. This is standard multi-key sort behavior.

The MERGE verb in COBOL requires all input files and the output file to have records of the same size. This is because MERGE combines already-sorted files into a single sorted output, and record size compatibility is essential for proper merging. The input files must be sorted on merge keys before MERGE executes, and key positions must match across files.