interface Computer
{
	void println(String text);
	String readLine();
}

class DesktopComputer implements Computer
{
	public void println(String text) { ... }
	public String readLine() { ... }
}


class LaptopComputer implements Computer
{
	public void println(String text) { ... }
	public String readLine() { ... }
}


class WearableComputer implements Computer
{
	private boolean isOn;

	public void println(String text) { ... }
	public String readLine() { ... }

	public void putOn() { this.isOn = true; }
	public void takeOff() { this.isOn = true; }
}

class Student
{
	// not so good
	// DesktopComputer computer;
	Computer computer;

	public Student(Computer computer) {
		this.setComputer(computer);
	}
}


class ComputerRoom
{
	// not so good
	// List<DesktopComputer> computers;
	List<Computer> computers;
}


new Student(new DesktopComputer());
new Student(new LaptopComputer());
new Student(new WearableComputer());

// marker interface: empty
interface Serializable {}

class MyClass implements Serializable { ... }



void f(int[] array) { ... }

f({1, 2, 3});			// wrong
f(new int[]{1, 2, 3});	// OK



new int[0]
new int[]{}
null	// this is something else



1000000000
1000000