Question

Which of the following Java statements contain variables whose values are modified? a) \(p=i+j+k+7\) b) System.out.printlnC "variables whose values are destroyed" ) : c) System.out.println( \(\left.^{\prime} a=5^{\prime \prime}\right)\) d) value \(=\) input.nextint ();

Short answer

Statements a and d involve variable value modification.

Step-by-step solution

Analyze Statement a

The statement \(p = i + j + k + 7\) is an assignment statement that assigns the sum of \(i\), \(j\), \(k\), and 7 to the variable \(p\). Here, the value of \(p\) is modified (or created). Other variables \(i\), \(j\), and \(k\) are used in a read-only manner.

Analyze Statement b

The statement `System.out.println("variables whose values are destroyed")` is a print statement that outputs a String. It does not involve any variable's value being modified.

Analyze Statement c

The statement `System.out.println('a=5')` is similar to the previous step in that it prints a String literal. It does not involve variable value modification.

Analyze Statement d

The statement `value = input.nextInt();` is an assignment statement that reads an integer from user input (`input.nextInt()`) and stores it in the variable `value`. This modifies the value (or initializes) of the variable `value`.

Key concepts

Variable Assignment in Java

In Java programming, variable assignment is a fundamental concept that refers to the process of allocating a value to a variable. This is typically done using the equals sign `=`. When you assign a value to a variable, you are either defining it for the first time or updating it with a new value. For instance, in the expression `p = i + j + k + 7;`, the variable `p` is assigned a new value. It gets the result of the sum of the variables `i`, `j`, `k`, and the constant `7`.
Variable assignment is crucial because it informs the program of what to store in memory. A variable can hold data such as integers, strings, or objects, and it is imperative to make sure that the data type of the value matches the variable type.

• The assignment operator is `=`.
• The left side should always be a variable name.
• The right side is an expression that evaluates to a value.

Handling User Input in Java

User input handling is a way to get data from users during the execution of a program. In Java, this can be accomplished through various methods, with the `Scanner` class being one of the most common ways. Using the `Scanner` class, you can read different types of input, such as strings and integers. The statement `value = input.nextInt();` showcases how to take integer input.
To use the Scanner class, you first need to create an instance of it, generally using `Scanner input = new Scanner(System.in);`. From there, you can call methods like `nextInt()` to read integers, `nextLine()` to read strings, and so forth.

• `System.in` is the standard input stream.
• `input.nextInt()` is used to read an integer from the input.
• `value` stores the user's input after reading.

Modifying Variable Values

Modifying a variable's value means changing what is stored in the variable after its initial assignment. This is an essential part of programming as it allows for dynamic processes. Modification occurs when you assign a new value to a previously established variable. For example, in `value = input.nextInt();`, the variable `value` is modified by receiving a new integer input from the user.
Another common context for modifications might include performing arithmetic operations or updating loop counters. Understanding how and when to modify variables is vital for keeping your programs responsive and interactive.

• Initial assignment is called variable initialization.
• Subsequent changes are termed variable modification.
• A variable can be modified multiple times throughout a program.