Question

Fill in the blanks in each of the following statements: a) Typically, ______________ statements are used for counter-controlled repetition and __________ statements for sentinel-controlled repetition. b) The do...while statement tests the loop-continuation condition __________ executing the loop's body; therefore, the body always executes at least once. c) The __________ statement selects among multiple actions based on the possible values of an integer variable or expression, or a String. d) The ______________ statement, when executed in a repetition statement, skips the remaining statements in the loop body and proceeds with the next iteration of the loop. e) The _________ operator can be used to ensure that two conditions are both true before choosing a certain path of execution. f) If the loop-continuation condition in a for header is initially _____________, the program does not execute the for statement's body. g) Methods that perform common tasks and do not require objects are called methods.

Short answer

a) 'for', 'while'; b) after; c) 'switch'; d) 'continue'; e) '&&'; f) false; g) 'static'

Step-by-step solution

Identify Counter-Controlled Statements

Counter-controlled repetition uses a counter variable and a specific number of iterations. The 'for' statement is typically used for this type of loop.

Identify Sentinel-Controlled Statements

Sentinel-controlled repetition uses a specific value to terminate the loop, often referred to as a sentinel value. The 'while' statement is commonly used for this type of loop.

Determine When do...while Checks its Condition

The 'do...while' statement tests its loop-continuation condition after the loop's body is executed, guaranteeing that the loop's body will run at least once.

Understand Multi-Path Selection Statements

The 'switch' statement is used to select among multiple actions based on different values of a variable.

Identify Loop Skipping Statements

The 'continue' statement is used within a loop body to skip the rest of the loop body and continue with the next iteration.

Recognize Logical Operators

The '&&' logical operator ensures that both conditions on its sides are true before proceeding in the execution path.

Know When for Loops Skip Execution

If a 'for' loop's continuation condition is false initially, the body of the loop doesn't execute.

Define Methods without Objects

Methods that are accessible without creating an instance of a class are called 'static' methods.

Key concepts

Counter-Controlled Repetition

In Java, counter-controlled repetition is a fundamental concept used for iterating a specific number of times. This is commonly achieved using a 'for' loop, where we initialize a counter variable, specify a loop-continuation condition, and determine the updating of the counter after each iteration. It looks something like this:

for (int i = 0; i < 10; i++) {
// Code to be repeated
}

Here, the loop begins with the counter 'i' at 0, continues to run as long as 'i' is less than 10, and increments 'i' by one in each iteration. This is ideal for scenarios where the exact number of repetitions is known beforehand, such as iterating through array elements.

Sentinel-Controlled Repetition

Sentinel-controlled repetition, on the other hand, differs from counter-controlled as it continues to loop until a certain condition, typically the value of the input, indicates that the end of the process has been reached. This is often achieved with a 'while' loop paired with a so-called sentinel value.

For example:

int input = scanner.nextInt();
while(input != sentinelValue) {
// Code to process the input
input = scanner.nextInt();
}

The sentinel-controlled loop keeps asking for input and processes it until an end-of-data value (the sentinel) is entered. This technique is particularly useful when the number of iterations is not known beforehand, such as reading a file until the end is reached.

The do...while Statement

A 'do...while' loop is slightly different from a regular 'while' loop because it executes the code block at least once before checking the continuation condition. This is because the condition is tested at the end of the loop rather than at the beginning. Here's the basic structure:

do {
// Code block to be executed
} while (loopContinuationCondition);

This loop will run the code inside the 'do' block and then check whether the condition is true to decide if another iteration is warranted. This control structure is helpful when the initial run of the loop's body is required regardless of the loop-continuation condition.

The Switch Statement

The 'switch' statement provides a multi-branch selection mechanism, allowing one to choose between several blocks of code to execute. The 'switch' works with an integer, character, or String expression and pairs this value with 'case' labels. An example statement would look like this:

switch (variable) {
case value1:
// Action for value1
break;
case value2:
// Action for value2
break;
// Additional cases
default:
// Default action
}

Each 'case' specifies an execution path, and the 'break' statement prevents the code from falling through to subsequent cases. The 'default' case is optional and executes if none of the specified cases match the variable's value.

The Continue Statement

When working with loops, sometimes we need to skip the current iteration and immediately proceed to the next one without completing the rest of the loop's body. The 'continue' statement performs this action.

For instance:

for (int i = 0; i < 10; i++) {
if (i % 2 == 0) {
continue; // Skip the rest of the loop for even numbers
}
// Code for odd numbers
}

Here, 'continue' directs the loop to skip the rest of the code block for even numbers and move directly to the next iteration. It's a handy way to improve efficiency by preventing unnecessary code execution.

Logical Operators

Java includes several logical operators that control the flow of execution by evaluating Boolean expressions. The most common ones are '&&' (logical AND), '||' (logical OR), and '!' (logical NOT). The '&&' operator, for instance, requires both conditions it combines to be true for the overall expression to be true.

Here's how you might use it:

if (condition1 && condition2) {
// Code to execute if both conditions are true
}

This structure with logical operators is frequently used in control statements to make complex decisions based on multiple criteria.

Static Methods

Static methods are those that can be invoked without needing an instance of a class. These methods are declared with the 'static' modifier and belong to the class rather than any object of the class. This makes static methods ideal for operations that don't require any data from an object instance.

An example of a static method is:

public static int add(int a, int b) {
return a + b;
}

This can be called using the class name itself, like ClassName.add(5, 3). Static methods are often implemented as helper methods or for utility-like functionality that is common across all instances of a class.