Java
public class Main {
public static void main(String[] args) {
System.out.println("Line one");
System.out.println("Line two");
}
}The rules
- Every statement ends with a semicolon.
- Blocks are wrapped in
{ }. - Java is case-sensitive:
myVarandmyvardiffer. - Class names use
PascalCase; methods and variables usecamelCase; constants useUPPER_SNAKE_CASE.
print vs println vs printf
Java
System.out.print("no newline");
System.out.println("with newline");
System.out.printf("Name: %s, Age: %d, Price: %.2f%n", "Sita", 21, 1250.5);Common format specifiers: %s string, %d integer, %f float,
%.2f two decimal places, %n newline, %% a literal percent.
Comments
Java
// single line
/* multi
line */
/**
* Javadoc comment — used to generate API documentation.
* @param name the person's name
* @return a greeting
*/Reading input
Java
import java.util.Scanner;
public class Main {
public static void main(String[] args) {
Scanner sc = new Scanner(System.in);
System.out.print("Enter your name: ");
String name = sc.nextLine();
System.out.print("Enter your age: ");
int age = sc.nextInt();
System.out.println("Hello " + name + ", age " + age);
sc.close();
}
}Watch out: nextInt() leaves the newline in the buffer, so a following
nextLine() returns an empty string. The usual fix is an extra
sc.nextLine() after reading a number.
Knowledge Check
4 questions — test your understanding
1
What is the difference between an ArrayList and a LinkedList?
2
What does `Collections.unmodifiableList()` return?
3
What is the difference between HashMap and TreeMap?
4
What does the enhanced for loop `for (String s : list)` do?