Java Programming - Beginnings

So fart: Printing, variables and types, user input, casting

How do you print “Hello World.”?

System.out.println("Hello world.");

How do you declare a variable that is all whole numbers and their negatives (integers)?

int num;

How do you declare a variable that is a real number that also has decimals?

double num;

How do you declare a variable that is a character of the alphabet?

char letter;

How do you declare a variable that represents a logical system that can only have one of two values: true/false, yes/no, etc?

boolean value;

How do you declare a variable that is composed of words

String words;

Why are strings unique?

Unlike int, double, boolean, or char, they are a non-primitive data type

User input for string?

String str = readLine(prompt);

User input for integer?

int num = readInt(prompt);

User input for double?

double myDouble = readDouble(prompt);

User input for boolean?

boolean bool = readBoolean(prompt);

Suppose you initialize two integer variables. How would you create variable sum, which represents the sum of both integers?

int sum = firstInteger + secondInteger;

Suppose a represents the int 20 and b represents the int 6. What would a / b result in?

Just 3; when dividing two integers, the result gets TRUNCATED.

If you divide two integers and the expected value is 3.9, what value does it truly become given the code is in Java?

Just 3; integer division always results in an integer and it is truncated, meaning rounding doesn’t occur

What is the result of 150 % 100

50

Is “#” an arithmetic operator

No; arithmetic means addition, subtraction, division, multiplication, and modulus

What is casting in Java?

Casting is turning a value of one type into another type.

What does (int) 9.9 simplify to?

9

How would you cast the double 10.9 to an int?

(int) 10.9 = 10;

How would you overcome integer division truncation?

Casting either the numerator or denominator as a double: 2 / (double) 3

While you could cast either the numerator or denominator for integer division, what is a more visually-appealing solution?

Casting outside of parentheses: (double) (2/3)

How do you round double values to the nearest integer value?

Add 0.5 to the double, then cast it to an integer will round it to the nearest integer.