java 16.静态static关键字修饰成员

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mb5fe5605983816 2021-09-18 01:08:00

文章标签 成员对象函数调用 static关键字成员变量类属性 文章分类 代码人生

static

在一个类中，如果使用static关键字来修饰类属性（成员变量），那这个变量就属于类，类里面的所有对象都可以共享这个变量。

什么意思呢？我们看一下代码就明白了：

现在有一个类Student

package static_demo;

public class Student {
private String name;
private  int age;
static String room;

public Student() {
System.out.println("调用空Student");
    }

public Student(String name, int age) {
System.out.println("调用带参Student");
this.name = name;
this.age = age;
    }

public String getName() {
System.out.println("调用getName方法");
return name;
    }

public void setName(String name) {
this.name = name;
    }

public int getAge() {
System.out.println("调用getAge方法");
return age;
    }

public void setAge(int age) {
this.age = age;
    }

public static String getRoom() {
System.out.println("调用getRoom方法");
return room;
    }

public static void setRoom(String room) {
Student.room = room;
    }
}

然后我们下面这个函数调用Student类实例化两个Student成员对象one和two、并且定义one.room= "101教室"，这里two可以不声明而直接使用！这就是因为在Student类中我们通过static来修饰room这个变量，room不是one对象的，虽然他对其做了声明，但是room是属于Student类的，不管创建几个Student的成员对象，成员之间都是共享一个room，这个room属于Student类。

package static_demo;

public class staticField {
public static void main(String[] args) {
Student one = new Student("郭靖",19);
one.room = "101教室";
System.out.println("姓名：" + one.getName() + ",年龄：" + one.getAge() + "所在教室：" + one.room);
Student two = new Student("黄蓉",16);
System.out.println("姓名：" + two.getName() + ",年龄：" + two.getAge() + "所在教室：" + one.room);
    }
}

在这个例子里，没有执行到空Student对象public Student()

下面我们实现这样一个效果：每次new Student对象都做一个加一操作，让学号递增。

也很简单，Student类代码如下

package static_demo;

public class Student {
private int no;  //学号
private String name;
private  int age;
static String room;
private static int noCounter = 0;  //学号计数器

public Student() {
System.out.println("调用空Student");
noCounter++;
    }

public Student(String name, int age) {
System.out.println("调用带参Student");
this.name = name;
this.age = age;
this.no = ++noCounter;
    }

public int getNo() {
return no;
    }

public void setNo(int no) {
this.no = no;
    }

public static int getNoCounter() {
return noCounter;
    }

public static void setNoCounter(int noCounter) {
Student.noCounter = noCounter;
    }

public String getName() {
System.out.println("调用getName方法");
return name;
    }

public void setName(String name) {
this.name = name;
    }

public int getAge() {
System.out.println("调用getAge方法");
return age;
    }

public void setAge(int age) {
this.age = age;
    }

public static String getRoom() {
System.out.println("调用getRoom方法");
return room;
    }

public static void setRoom(String room) {
Student.room = room;
    }
}

调用类的代码

package static_demo;

public class staticField {
public static void main(String[] args) {
Student one = new Student("郭靖",19);
one.room = "101教室";
System.out.println("姓名：" + one.getName()
+ ",年龄：" + one.getAge() + "所在教室：" + one.room + "，学号：" + one.getNo());
Student two = new Student("黄蓉",16);
System.out.println("姓名：" + two.getName()
+ ",年龄：" + two.getAge() + "所在教室：" + two.room + "，学号：" + two.getNo());
Student oyf = new Student("欧阳锋",56);
System.out.println("欧阳锋的学号是：" + oyf.getNo());
Student yg = new Student("杨过",14);
System.out.println("杨过的学号是：" + yg.getNo());
Student xln = new Student("小龙女",16);
System.out.println("小龙女的学号是：" + xln.getNo());
    }
}