Person.java

public class Person {

	public static int count;
	String name;

	public Person(String name) {
		this.name = name;
		count++;
	}

	public static int getCount(){
		return count;
	}

}

Main.java

public class Main {

	public static void main(String[] args) {
		// TODO: 给Person类增加一个静态字段count和静态方法getCount，统计实例的个数
		Person p1 = new Person("小明");
		System.out.println(Person.getCount()); // 1
		Person p2 = new Person("小红");
		System.out.println(Person.getCount()); // 2
		Person p3 = new Person("小军");
		System.out.println(Person.getCount()); // 3
	}

}