无法从 Java 中的另一个类访问变量？

Question

我正在尝试调用我在另一个类中创建的变量 numFriends，但是当我尝试这样做时，它显示“numFriends 无法解析为变量”。每次添加新朋友时变量都会增加，我想在我的测试类中显示它。这是我的代码：

一级

public class Person {

    private String fullName;
    private char gender; 
    private int age;

    public static int numFriends = 0;

    public Person(String nm, char gen, int a) {
        fullName = nm;
        gender = gen;
        age = a; 
        numFriends++;
    }

    public void setName(String nm) {
        fullName = nm;
    }

    public void setAge(int a) {
        age = a;
    }

    public int getAge() {
        return age;
    }

    public void setGender(char g) {
        gender = g;
    }

    public String toString() {
        return (fullName + ", gender = " + gender + ", age = " + age );
    }

}

第二类（可执行）

public class TestPerson {

    public static void main(String[] args) {

        System.out.println(numFriends + " people at first");

        Person p1 = new Person("Otto Mattik", 'M', 22);
        p1.setName("Otto Mattik");
        p1.setGender('M');
        p1.setAge(22);
        System.out.println("Person Full Name = " + p1);

        Person p2 = new Person("Anna Bollick", 'F', 19);
        p2.setName("Anna Bollick");
        p2.setGender('F');
        p2.setAge(19);
        System.out.println("Person Full Name = " + p2);


        Person p3 = new Person("Dick Tator", 'M', 33);
        p3.setName("Dick Tator");
        p3.setGender('M');
        p3.setAge(33);
        System.out.println("Person Full Name = " + p3);

        changeName(p2, "Anna Bollik-Mattik");

        Person[] people = {
                p1, p2, p3
        };

        agePersons(people, 5);

        System.out.println("\n" + numFriends + " people after 5 years");

        for (Person person : people)
            System.out.println("Person fullName: " + person);

    }

    public static void changeName(Person p, String name) {
        p.setName(name);
    }

    public static void agePersons(Person[] people, int years) {
        for (Person person : people)
            person.setAge(person.getAge() + years);
    }
}

Answer 1

你需要说Person.numFriends。这是因为 numFriends 是 Person 类的静态成员，所以需要使用 Person 类来引用 numFriends。