第2节：java继承多态这一篇就够了

package test;

public class Human
{
    /**
     * constructor
     */
    public Human(int h)
    {
        this.height = h;
        System.out.println("I'm born");
        Human.population +=1;
    }

    /**
     * accessor
     */
    public int getHeight()
    {
        return this.height;
    }

    /**
     * mutator
     */
    public void growHeight(int h)
    {
        this.height = this.height + h;
    }

    public static int getPopulation()
    {
        return Human.population;
    }

    private int height;
    private static int population; // 类内部使用
    public static boolean is_mammal = true; // 类外部可以直接使用
}

import test.Human;

public class testAgain {
    public static void main(String[] args)
    {
        Human aPerson = new Human(180);
        System.out.println(aPerson.getHeight());
        System.out.println(Human.is_mammal);
        System.out.println(aPerson.getPopulation());
    }
}