oop concepts and lang basics

Question 1

Real-world objects contain ___ and ___.

Answer 1

Real-world objects contain state and behavior.

Question 2

A software object’s state is stored in ___.

Answer 2

A software object’s state is stored in fields.

Question 3

A software object’s behavior is exposed through ___.

Answer 3

A software object’s behavior is exposed through methods.

Question 4

Hiding internal data from the outside world, and accessing it only through publicly exposed methods is known as data ___.

Answer 4

Hiding internal data from the outside world, and accessing it only through publicly exposed methods is known as data encapsulation.

Question 5

A blueprint for a software object is called a ___.

Answer 5

A blueprint for a software object is called a class.

Question 6

Common behavior can be defined in a ___ and inherited into a ___ using the ___ keyword.

Answer 6

Common behavior can be defined in a superclass and inherited into a subclass using theextends keyword.

Question 7

A collection of methods with no implementation is called an ___.

Answer 7

A collection of methods with no implementation is called an interface.

Question 8

A namespace that organizes classes and interfaces by functionality is called a ___.

Answer 8

A namespace that organizes classes and interfaces by functionality is called a package.

Question 9

The term API stands for ___?

Answer 9

The term API stands for Application Programming Interface.

Question 10

The term “instance variable” is another name for ___.

Answer 10

The term “instance variable” is another name for non-static field.

Question 11

The term “class variable” is another name for ___.

Answer 11

The term “class variable” is another name for static field.

Question 12

A local variable stores temporary state; it is declared inside a ___.

Answer 12

A local variable stores temporary state; it is declared inside a method.

Question 13

A variable declared within the opening and closing parenthesis of a method signature is called a ____.

Answer 13

A variable declared within the opening and closing parenthesis of a method is called aparameter.

Question 14

What are the eight primitive data types supported by the Java programming language?

Answer 14

What are the eight primitive data types supported by the Java programming language?byte, short, int, long, float, double, boolean, char

Question 15

Character strings are represented by the class ___.

Answer 15

Character strings are represented by the class java.lang.String.

Question 16

An ___ is a container object that holds a fixed number of values of a single type.

Answer 16

An array is a container object that holds a fixed number of values of a single type.

Question 17

Consider the following code snippet.

arrayOfInts[j] > arrayOfInts[j+1]

Which operators does the code contain?

Answer 17

Answer: >, +

Question 18

Consider the following code snippet:

int i = 10;
int n = i++%5;

Question: What are the values of i and n after the code is executed?

Question: What are the final values of i and n if instead of using the postfix increment operator (i++), you use the prefix version (++i))?

Answer 18

Answer: i is 11, and n is 0.

Answer: i is 11, and n is 1.

Question 19

To invert the value of a boolean, which operator would you use?

Answer 19

The logical complement operator “!”.

Question 20

Which operator is used to compare two values, = or == ?

Answer 20

The == operator is used for comparison, and = is used for assignment.

Question 21

Explain the following code sample: result = someCondition ? value1 : value2;

Answer 21

This code should be read as: “If someCondition is true, assign the value ofvalue1 to result. Otherwise, assign the value of value2 to result.”

Question 22

Change the following program to use compound assignments:

1. ```
   class ArithmeticDemo { public static void main (String[] args){ int result = 1 + 2; // result is now 3 System.out.println(result); result = result - 1; // result is now 2 System.out.println(result); result = result * 2; // result is now 4 System.out.println(result); result = result / 2; // result is now 2 System.out.println(result); result = result + 8; // result is now 10 result = result % 7; // result is now 3 System.out.println(result); } }
   ~~~

Answer 22

class ArithmeticDemo { public static void main (String[] args){ int result = 3; System.out.println(result); result -= 1; // result is now 2 System.out.println(result); result \*= 2; // result is now 4 System.out.println(result); result /= 2; // result is now 2 System.out.println(result); result += 8; // result is now 10 result %= 7; // result is now 3 System.out.println(result); } }

Question 23

In the following program, explain why the value “6” is printed twice in a row:

class PrePostDemo { public static void main(String[] args){ int i = 3; i++; System.out.println(i); // "4" ++i; System.out.println(i); // "5" System.out.println(++i); // "6" System.out.println(i++); // "6" System.out.println(i); // "7" } }

Answer 23

The code System.out.println(++i); evaluates to 6, because the prefix version of ++evaluates to the incremented value. The next line, System.out.println(i++);evaluates to the current value (6), then increments by one. So “7” doesn’t get printed until the next line.

Question 24

Operators may be used in building ___, which compute values.

Answer 24

Operators may be used in building expressions, which compute values.

Question 25

Expressions are the core components of \_\_\_.

Answer 25

Expressions are the core components of statements.

Question 26

Statements may be grouped into \_\_\_.

Answer 26

Statements may be grouped into blocks.

Question 27

The following code snippet is an example of a ___ expression. 1 \* 2 \* 3

Answer 27

The following code snippet is an example of a compound expression. 1 \* 2 \* 3

Question 28

Statements are roughly equivalent to sentences in natural languages, but instead of ending with a period, a statement ends with a \_\_\_.

Answer 28

Statements are roughly equivalent to sentences in natural languages, but instead of ending with a period, a statement ends with a semicolon.

Question 29

A block is a group of zero or more statements between balanced ___ and can be used anywhere a single statement is allowed.

Answer 29

A block is a group of zero or more statements between balanced braces and can be used anywhere a single statement is allowed.

Question 30

Identify the following kinds of expression statements: * `aValue = 8933.234;` * `aValue++;` * `System.out.println("Hello World!");` * `Bicycle myBike = new Bicycle();`

Answer 30

Identify the following kinds of expression statements: * `aValue = 8933.234; // assignment statement` * `aValue++; // increment statement` * `System.out.println("Hello World!"); // method invocation statement` * `Bicycle myBike = new Bicycle(); // object creation statement`

Question 31

The most basic control flow statement supported by the Java programming language is the ___ statement.

Answer 31

The most basic control flow statement supported by the Java programming language is theif-then statement.

Question 32

The ___ statement allows for any number of possible execution paths.

Answer 32

The switch statement allows for any number of possible execution paths.

Question 33

The ___ statement is similar to the while statement, but evaluates its expression at the ___ of the loop.

Answer 33

The do-while statement is similar to the while statement, but evaluates its expression at the bottom of the loop.

Question 34

How do you write an infinite loop using the for statement?

Answer 34

``` for ( ; ; ) { } ```

Question 35

How do you write an infinite loop using the while statement?

Answer 35

``` while (true) { } ```

Question 36

Consider the following code snippet. ``` if (aNumber \>= 0) if (aNumber == 0) System.out.println("first string"); else System.out.println("second string"); System.out.println("third string"); ``` 1. **Exercise:** What output do you think the code will produce if `aNumber` is 3?

Answer 36

``` second string third string ```

Question 37

Write a test program containing the previous code snippet; make`aNumber` 3. What is the output of the program? Is it what you predicted? Explain why the output is what it is. In other words, what is the control flow for the code snippet?

Answer 37

**Solution:** [`NestedIf`](https://docs.oracle.com/javase/tutorial/java/nutsandbolts/QandE/NestedIf.java) ``` second string third string ``` 3 is greater than or equal to 0, so execution progresses to the second `if`statement. The second `if` statement's test fails because 3 is not equal to 0. Thus, the `else` clause executes (since it's attached to the second `if` statement). Thus,`second string` is displayed. The final `println` is completely outside of any `if`statement, so it always gets executed, and thus `third string` is always displayed.

Question 38

Using only spaces and line breaks, reformat the code snippet to make the control flow easier to understand. ## Footnote ``` if (aNumber \>= 0) if (aNumber == 0) System.out.println("first string"); else System.out.println("second string"); System.out.println("third string"); ```

Answer 38

``` if (aNumber \>= 0) if (aNumber == 0) System.out.println("first string"); else System.out.println("second string"); System.out.println("third string"); ```

Question 39

Use braces `{` and `}` to further clarify the code and reduce the possibility of errors by future maintainers of the code. ## Footnote ``` if (aNumber \>= 0) if (aNumber == 0) System.out.println("first string"); else System.out.println("second string"); System.out.println("third string"); ```

Answer 39

``` if (aNumber \>= 0) { if (aNumber == 0) { System.out.println("first string"); } else { System.out.println("second string"); } } System.out.println("third string"); ```