Lesson 2 of 9

Variables and types

In Java you declare each variable's type and it can't change later. This is static typing, and it lets the compiler catch many mistakes before the program runs.

JAVA · inside main

int age = 21;
double gpa = 4.5;
String name = "Sara";
boolean isMis = true;
char grade = 'A';
System.out.println(name + " " + age + " " + gpa + " " + isMis + " " + grade);

Output

Sara 21 4.5 true A

int	whole number: 21
double	decimal: 4.5
String	text in " ": "Sara"
boolean	true or false
char	one character in ' ': 'A'

Watch division: dividing two ints gives an int and drops the fraction. Cast one of them to double for a decimal result.

JAVA · inside main

int a = 7, b = 2;
System.out.println(a / b);
System.out.println(a % b);
System.out.println((double) a / b);
System.out.println(a + b + "!");
System.out.println("!" + a + b);

Output

3
1
3.5
9!
!72

Watch out+ is read left to right: a + b + "!" adds the numbers first (9!), while "!" + a + b turns everything into text from the start (!72).

Same idea in both languages

Python

name = "Sara"
age = 21
gpa = 4.5

Java

String name = "Sara";
int age = 21;
double gpa = 4.5;