Differences between Java interfaces and abstract classes

Basic grammatical differences

public interface Animal {
    // 所有动物都会吃
    public void eat();

    // 所有动物都会飞
    public void fly();
}

public abstract class Animal {
    // 所有动物都会吃
    public abstract void eat();

    // 所有动物都会飞
    public void fly(){};
}

public class concreteAnimal implements Animal {
    // 所有动物都会吃
    public void eat(){}

    // 所有动物都会飞
    public void fly(){}
}

public class concreteAnimal extends Animal {
    // 所有动物都会吃
    public void eat(){}

    // 所有动物都会飞
    public void fly(){}
}

Differences in design ideas

public interface Animal {
    // 所有动物都会吃
    public void eat();
}

public abstract class Animal {
    // 所有动物都会吃
    public abstract void eat();
}

public class concreteAnimal implements Animal {
    // 所有动物都会吃
    public void eat(){}
}

public class concreteAnimal extends Animal {
    // 所有动物都会吃
    public void eat(){}
}

public interface Animal {
    // 所有动物都会吃
    public void eat();

    // 所有动物都会飞
    public void fly();
}

public abstract class Animal {
    // 所有动物都会吃
    public abstract void eat();

    // 所有动物都会飞
    public void fly(){};
}

public interface AnimaiFly {
    // 所有动物都会飞
    public void fly();
}

public class concreteAnimal implements Animal,AnimaiFly {
    // 所有动物都会吃
    public void eat(){}

    // 动物会飞
    public void fly();
}

public abstract class AnimaiFly {
    // 动物会飞
    public void fly();
}

public abstract class AnimaiFly extends Animal {
    // 动物会飞
    public void fly();
}

public abstract class Animal {
    // 所有动物都会吃
    public abstract void eat();
}

public interface AnimaiFly {
    // 动物会飞
    public void fly();
}

public class concreteAnimal extends Animal implements AnimaiFly {
    // 所有动物都会吃
    public void eat(){}

    // 动物会飞
    public void fly();
}

public interface Animal {
    // 所有动物都会吃
    public abstract void eat();
}

public abstract class AnimaiFly {
    // 动物会飞
    public void fly(){};
}

public class concreteAnimal extends AnimaiFly implements Animal {
    // 所有动物都会吃
    public void eat(){}

    // 动物会飞
    public void fly();
}