Chapter 2 - In person Class

Question 1

What’s the object in System.out.println (“Whatever”)?
What’s the method?
What’s the parameter?

Answer 1

system.out

println is the method.

Question 2

What’s the difference between Primitive data (for python and java).

Answer 2

Python figures it out for you, in java you have to be specific.

Question 3

How many types of primitive data are there? (can they be negative)

Answer 3

There are four integers. Two of them float, double. One of them are char, and the other boolean (yes).

Question 4

Why do computers approximate? How can that be a problem.

Answer 4

Because computers are limited. This can cause an issue when you are calculating total cost that need decimals.

Question 5

What happens when you add 1 to an integer type of 2147483647?

Answer 5

It rolls over and gives you -2147483648. So you went from billionaire to owing 2 billion. This is why it’s so important to know the type of data the integer is saved in. Compare that the cost of using more bits with type long.

Question 6

What is the difference between using ‘ and “ in Java? What language did Java come from?

Answer 6

You use single quotation mark for characters, where the uppercase and lowercase are different. Strings in Java use double quotation marks.

Java came from C.

Question 7

When creating a variable in java do you have to specify the data type (different than python)?

Answer 7

Yes.

Question 8

What’s a literal? Give an example of a string literal.

Answer 8

It’s simply a value. “Hello” is a string literal.

Question 9

Is an expression a program statement?

Answer 9

No, they cannot exist by themselves. They are part of statements that end with a semi-colon ( ; ).

“Hello” + “World” is an expression but not a statement. String s = “Hello” + “World”; is a statement.

Question 10

What is the %, a modulus (mod) operator? Why is it important?

Answer 10

It calculates the remainder. It’s important when we’re counting lists and telling the program to go back to the beginning after Remainder hits 0.

Question 11

What part of this is the expression?

result = total + count / max - offset;

Answer 11

Everything to the right of result is the expression of the statement.

Question 12

How do you create a constant in Java? What is the style used for a CONSTANT?

Answer 12

add a final in front of it. final int var1 = 1;

The style is to capitalize it.

Question 13

What do you need to know about data conversion? For example in one we may want to treat an integer as a floating point. (Java is a strongly typed language).

Answer 13

The data conversions do not change the type of variable. They do not affect the original variable or the original data value. You must be careful not to lose data value when going from wider to narrower type.

Question 14

What are the decrement operators ++ or –? Where will you see this all the time? It’s very common to use i for the outer loop, j for the next inner, and k for the next… and so forth.

Answer 14

count = 4. count++; is not the same thing as count = count +1; Count ++; is faster and adds only 1.
count++ is not the same as ++count.

total = count ++; Total becomes 4 first and then count++ becomes 5 after.

total = ++count; both Total and Count become 5.

We see ++ in loops all the time. for (int i = 0; i< 10 , i++)

Question 15

What are some assignment operators like +=? i.e. num += count;

Why is it important to learn this?

Answer 15

num += count; is equivalent to num = num + count.

This is because most of your job will not to start from scracth; but most likely fix other’s “crappy” coding.

Question 16

What are narrowing and widening conversions? When can it happen automatically?

Answer 16

It can happen automatically when widening but not when narrowing.

Question 17

What are the three types of conversions? What is SOP?

Answer 17

1- assignment conversion.
2- promotion.
3- casting. (i.e. type casing when you place a ) in front of the int). when widening it’s not typecasting. Typecasting is forcing for a type to narrow.

SOP - system output public.

Question 18

What is the difference between using = sign and == sign?

Answer 18

= sign is an assignment. == is used to compare true or false.

Question 19

Why is casting the most powerful and most dangerous technique for conversion?

Answer 19

Casting is not going to check the types. It’s going to widen or narrow. put a parentheses in front of the value being converted.

Typecast has higher precedence. Use parentheses.

Question 20

How can you clarify (self-document) this statement, although it doesn’t change the result? result = (float) total / count;

Answer 20

result = ( (float) total ) / count;

int a = 97;
char c = ‘ ‘;
c = (char)a;

You cannot typecast a string literal like 1.

If char c = a, then c++ is equal to b.

Question 21

What is an interactive program? How do you add input?

Answer 21

The scanner class provides convenient methods for reading input. SYSTEM.IN is the keyboard!!!

Question 22

How do you create a scanner object? Where do you see them? DO WE NEED TO IMPORT?

Answer 22

All objects are created using the word NEW. Here we create a avg_input variable.

Scanner avg_input= new Scanner (System.in)
answer = avg_input.nextLine()

Yes, we need to IMPORT JAVA.UTIL.SCANNER;

Question 23

I will only use methods within the yellow boxes.

Answer 23

Scanner is on page 87.

import java.util Scanner;

String message;
Scanner scan;

scan = new Scanner (System.in);
System.out.println (“Enter a line of text”); // prompt the user
message = scan.nextLine();
scan.close();

Question 24

How can you use the scanner class to input integers or doubles.

Answer 24

double message1, message2;
Scanner scan;

System.out.println (“Enter two numbers separated by space and then hit enter”);

message1 = scan.nextInt();
message2 = scan.nextInt();

System.out.println (message1 + message2 + 5 + 7)

scan.close();

Question 25

What is the angry programmer (violent outburst programmer) rule?

Answer 25

Write your code and submit your work with the assumption it’s going to be read by an angry person who is prone to blowing up and coming after you with violence.

Question 26

What is a trace?

Answer 26

It’s to track the variable values as the program executes code line by line. It is something you can do manually or ask Eclipse to do it.