Java: What is the difference between abstract class and interface?

1abstract class Animal {
2    protected String name;
3
4    public Animal(String name) {
5        this.name = name;
6    }
7
8    public void sleep() {
9        System.out.println(name + " sleeping");
10    }
11
12    public abstract void makeSound();
13}
14
15class Dog extends Animal {
16    public Dog(String name) { super(name); }
17
18    @Override
19    public void makeSound() {
20        System.out.println("Bark!");
21    }
22}
23
24Dog d = new Dog("Rex");
25d.sleep();      // Rex sleeping
26d.makeSound(); // Bark!

1interface Swimmable {
2    void swim();
3
4    default void float_() {
5        System.out.println("Floating");
6    }
7}
8
9interface Flyable {
10    void fly();
11}
12
13class Duck extends Animal implements Swimmable, Flyable {
14    public Duck(String name) { super(name); }
15
16    @Override
17    public void makeSound() { System.out.println("Quack!"); }
18
19    @Override
20    public void swim() { System.out.println("Swimming"); }
21
22    @Override
23    public void fly() { System.out.println("Flying"); }
24}
25
26Duck duck = new Duck("Donald");
27duck.swim();  // Swimming
28duck.fly();   // Flying
29duck.float_(); // Floating (default)