Java: class , objects

Java: class , objects
1 Inheritance(继承)的关键字extends
class MountainBike extends Bicycle {
}
但是不能多重继承。不过可以通过implements多个interface来实现类似的东西
2 interface
interface Bicycle {
       void changeCadence(int newValue);   // wheel revolutions per minute
       void changeGear(int newValue);
       void speedUp(int increment);
       void applyBrakes(int decrement);
}
class ACMEBicycle implements Bicycle {
   // remainder of this class implemented as before
}
可实现(implements)多个interface
class MyClass extends MySuperClass implements YourInterface {
    //field, constructor, and method declarations
}
means that MyClass is a subclass of MySuperClass and that it implements the YourInterface interface
3 package
A package is a namespace that organizes a set of related classes and interfaces.
4 Access Modifier
public, private, protected
public class Bicycle {
     private int cadence;
     public int aag;
     public void test();
}
每个field或method都必须单独修饰
 
Access Levels
ModifierClassPackageSubclassWorld
public
Y
Y
Y
Y
protected
Y
Y
Y
N
no modifier
Y
Y
N
N
private
Y
N
N
N
约定：
class 名字的第一个字母大写; method第一个word是动词
5 Constructors
The compiler automatically provides a no-argument, default constructor for any class without constructors.
This default constructor will call the no-argument constructor of the superclass.
6 method & parameter
The Java programming language doesn't let you pass methods into methods. But you can pass an object into a method and then invoke the object's methods.
 can Returning a Class or Interface??
7 this : current object
public class Point {
public int x = 0; //field可以这样初始化
public int y = 0;