Question

Assume that i = 1, j = 2, k = 3 and m = 2. What does each of the following statements print? a) System.out.println( i == 1 ); b) System.out.println( j == 3 ); c) System.out.println( ( i >= 1 ) && ( j < 4 ) ); d) System.out.println( ( m <= 99 ) & ( k < m ) ); e) System.out.println( ( j >= i ) || ( k == m ) ); f) System.out.println( ( k + m < j ) | ( 3 - j >= k ) ); g) System.out.println( !( k > m ) );

Short answer

a) true, b) false, c) true, d) false, e) true, f) false, g) false.

Step-by-step solution

Evaluate a)

The expression is \( i == 1 \). Since \( i \) is given as 1, the expression evaluates to \( \text{true} \).

Evaluate b)

The expression is \( j == 3 \). Since \( j \) is given as 2, the expression evaluates to \( \text{false} \).

Evaluate c)

The expression is \( ( i >= 1 ) \&\& ( j < 4 ) \). We evaluate each: \( i >= 1 \) is \( \text{true} \) (since \( i = 1 \)) and \( j < 4 \) is \( \text{true} \) (since \( j = 2 \)). Since both are true, the result is \( \text{true} \).

Evaluate d)

The expression is \( ( m <= 99 ) \& ( k < m ) \). We evaluate each: \( m <= 99 \) is \( \text{true} \) (since \( m = 2 \)) and \( k < m \) is \( \text{false} \) (since \( k = 3 \) and \( m = 2 \)). As the second part is false, the result is \( \text{false} \).

Evaluate e)

The expression is \( ( j >= i ) || ( k == m ) \). We evaluate each: \( j >= i \) is \( \text{true} \) (since \( j = 2 \) and \( i = 1 \)) and \( k == m \) is \( \text{false} \) (since \( k = 3 \) and \( m = 2 \)). The first part is true, so the result is \( \text{true} \).

Evaluate f)

The expression is \( ( k + m < j ) \mid ( 3 - j >= k ) \). We evaluate each: \( k + m < j \) is \( \text{false} \) (since \( 3 + 2 ot< 2 \)) and \( 3 - j >= k \) is \( \text{false} \) (since \( 3 - 2 ot\geq 3 \)). Since both are false, the result is \( \text{false} \).

Evaluate g)

The expression is \( !( k > m ) \). The negation of \( k > m \) is \( \text{true} \) since \( k = 3 \) and \( m = 2 \), so \( k > m \) is \( \text{true} \) and negating it gives \( \text{false} \).

Key concepts

Boolean Expressions

A Boolean expression in Java is a statement that evaluates to either true or false. These expressions involve relational operators such as `==`, `!=`, `<`, `<=`, `>`, and `>=` to compare two values. The essence of Boolean expressions is to test conditions in a program and decide which path to execute next.
In the exercise example, when we write `i == 1`, we are checking if the variable `i` is equal to 1. Since it genuinely is, the expression results in `true`. Java recognizes these types of expressions and evaluates them according to specified conditions. This evaluation is key in programming, especially when set conditions need to control the flow of operations. Java uses Boolean expressions extensively in loops, if-else conditions, and other logical structures. Understanding them is essential, so you're able to craft clear and efficient flow in your code.

Logical Operators

In Java, logical operators are used to combine or negate Boolean expressions. These operators include `&&` (logical AND), `||` (logical OR), and `!` (logical NOT). By using these operators, you can construct complex decision-making structures. - **Logical AND (`&&`)**: Both conditions must be true for the overall expression to be true. In our example, `(i >= 1) && (j < 4)` checks if both conditions are satisfied. Given both `i >= 1` and `j < 4` are true, the combined condition also results in true.
- **Logical OR (`||`)**: At least one condition needs to be true for the result to be true. In the case of `(j >= i) || (k == m)`, since `j >= i` holds true, the entire expression is true.
- **Logical NOT (`!`)**: This operator negates the result of a Boolean expression. For example, `!(k > m)` negates the true result of `k > m`, thus evaluating it to false. These operators are crucial in decision-making processes where multiple conditions need consideration simultaneously. Combining simple statements using logical operators allows programmers to precisely define how and when certain pieces of code should run.

Conditional Statements

Conditional statements in Java use Boolean expressions and logical operators to dictate the flow of execution in a program. These include `if`, `else if`, `else`, `switch`, etc. Conditional statements let programmers execute particular code blocks or actions based on whether conditions meet predefined criteria.
- **If-Else Statements**: They check a condition and execute a block of code if the condition is true. If `i == 1` and the test is within an if-statement, the body following the `if` block will run when `i` equals 1.
- **Switch Statements**: Used for more complex decision trees where a single variable may lead to multiple different outcomes. A typical use case might be deciding what operations to perform based on the value of a variable or expression.
Conditional execution controls are the backbone of decision-making in Java applications. Knowing how to form effective conditional statements ensures that your programs run efficiently and correctly under a variety of conditions. By mastering these structures, you gain the ability to make your applications adaptable and dynamic based on changing circumstances or input.