JAVA类与对象（五）----对象的生成、使用

对象的生成

创建一个对象包括对象的声明、实例化、初始化三部分。

1.声明-----类名对象名

　　声明并不是为对象分配内存空间，而只是分配一个引用空间。对象的引用类似于指针，是32位的地址空间，它的值指向一个中间的数据结构，它储存有关数据类型的信息以及当前对象所在的堆的地址，而对于对象所在的实际的内存地址是不可操作的，这就保证了安全性。

2.实例化

　　运算符new为对象分配内存空间，它调用对象的构造方法，返回引用。一个类的不同对象分别占用着不同的内存空间。

3.生成

　　执行构造方法进行初始化，根据参数不同调用相应的构造方法。

注意：如果类中没有构造方法，系统会自动调用默认的构造方法。默认的构造方法是无参数的。如果类中定义了构造方法，则必须使用类中定义的构造方法，否则会出错！

例：

class Student{
        float height,weight;
        String head,ear,hand,foot,mouth;
        Student()
        {
            height=0;
            weight=0;
            head="myhead";
            ear="myear";
            hand="myhead";
            foot="myfoot";
            mouth="mymouth";
            System.out.println("new Student ok!!!");
        }
    }

public class Man{
    public static void main(String args[]){
        Student zhangsan=new Student();
    }
}

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对象的使用

　　对象不仅可以改变自己变量的状态，而且还拥有使用创建它的那个类中的方法的能力。对象通过这些方法可以产生一定的行为，通过运算符“.”可以实现对变量和方法的访问。而变量和方法通过设置的权限来限制其他对象对自身的访问。

1.对象调用自己的变量

对象名.变量名

2.对象调用自己的方法

　对象名.方法名（参数）；

例：

class Person{
        float height,weight;
        String head,ear,hand,foot,mouth;
        Person()
        {
            height=175;
            weight=70;
            head="myhead";
            ear="myear";
            hand="myhead";
            foot="myfoot";
            mouth="mymouth";
            System.out.println("new Student ok!!!");
        }
        void speak(String s)
        {
            System.out.println("say:"+s);
        }
    }

public class Human{
    public static void main(String args[]){
        Person zhangsan=new Person();
        zhangsan.speak("hello java!!!");
        Person lisi=new Person();
        lisi.ear="大耳朵";
        lisi.speak("I am studying java!!!");
    }
}

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