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()); } }
输出
调用带参Student
调用getName方法
调用getAge方法
姓名:郭靖,年龄:19所在教室:101教室,学号:1
调用带参Student
调用getName方法
调用getAge方法
姓名:黄蓉,年龄:16所在教室:101教室,学号:2
调用带参Student
欧阳锋的学号是:3
调用带参Student
杨过的学号是:4
调用带参Student
小龙女的学号是:5