Java面向对象基础实例详解

public class Person {
    // 属性（成员变量）
    String name;
    int age;
    String gender;
    // 方法（成员方法）
    void introduce() {
        System.out.println("大家好，我叫" + name + "，今年" + age + "岁。");
    }
    void eat() {
        System.out.println(name + "正在吃饭。");
    }
    void sleep() {
        System.out.println(name + "正在睡觉。");
    }
}

public class VariableScope {
    // 成员变量：定义在类中，整个类都能访问
    String memberVar = "我是成员变量";
    void testMethod() {
        // 局部变量：定义在方法中，只在方法内有效
        String localVar = "我是局部变量";
        System.out.println(memberVar);  // 可以访问
        System.out.println(localVar);   // 可以访问
    }
    void anotherMethod() {
        System.out.println(memberVar);  // 可以访问
        // System.out.println(localVar);  // 编译错误！无法访问
    }
}

public class ObjectDemo {
    public static void main(String[] args) {
        // 创建Person对象
        Person person1 = new Person();
        person1.name = "张三";
        person1.age = 20;
        person1.gender = "男";
        // 调用对象的方法
        person1.introduce();  // 大家好，我叫张三，今年20岁。
        person1.eat();        // 张三正在吃饭。
        // 创建第二个对象
        Person person2 = new Person();
        person2.name = "李四";
        person2.age = 22;
        person2.gender = "女";
        person2.introduce();  // 大家好，我叫李四，今年22岁。
    }
}

public class Student {
    String name;
    int age;
    // 如果不写任何构造函数，Java自动提供：
    // public Student() {}
}

public class Student {
    String name;
    int age;
    String school;
    // 无参构造函数
    public Student() {
        System.out.println("创建了一个学生对象");
    }
    // 带参数的构造函数
    public Student(String name, int age, String school) {
        this.name = name;
        this.age = age;
        this.school = school;
    }
    // 部分参数的构造函数
    public Student(String name, int age) {
        this.name = name;
        this.age = age;
        this.school = "未知学校";
    }
    void introduce() {
        System.out.println("我叫" + name + "，今年" + age + "岁，在" + school + "上学。");
    }
}

public class ConstructorOverloadDemo {
    public static void main(String[] args) {
        // 使用无参构造函数
        Student s1 = new Student();
        s1.introduce();  // 输出默认值
        // 使用全参构造函数
        Student s2 = new Student("张三", 18, "北京大学");
        s2.introduce();  // 张三的介绍
        // 使用部分参数构造函数
        Student s3 = new Student("李四", 20);
        s3.introduce();  // 李四的介绍，学校为"未知学校"
    }
}

public class Person {
    String name;
    int age;
    public Person(String name, int age) {
        // this.name 是成员变量
        // name 是局部变量（参数）
        this.name = name;
        this.age = age;
    }
    public void setName(String name) {
        this.name = name;  // 区分成员变量和参数
    }
    public String getName() {
        return this.name;
    }
}

public class BankAccount {
    private String accountNumber;
    private double balance;
    private String owner;
    public BankAccount(String accountNumber, String owner, double initialBalance) {
        this.accountNumber = accountNumber;
        this.owner = owner;
        this.balance = initialBalance;
    }
    // getter方法
    public String getAccountNumber() {
        return accountNumber;
    }
    public double getBalance() {
        return balance;
    }
    // setter方法（带验证）
    public boolean deposit(double amount) {
        if (amount > 0) {
            balance += amount;
            System.out.println("存款成功，余额：" + balance);
            return true;
        } else {
            System.out.println("存款金额必须大于0");
            return false;
        }
    }
    public boolean withdraw(double amount) {
        if (amount > 0 && amount <= balance) {
            balance -= amount;
            System.out.println("取款成功，余额：" + balance);
            return true;
        } else {
            System.out.println("取款金额无效或余额不足");
            return false;
        }
    }
}

public class Student {
    String name;
    static String school;  // 静态变量，所有学生共享
    public Student(String name) {
        this.name = name;
    }
}
public class StaticDemo {
    public static void main(String[] args) {
        Student.school = "北京大学";  // 通过类名访问
        Student s1 = new Student("张三");
        Student s2 = new Student("李四");
        System.out.println(s1.name + "的学校：" + s1.school);  // 北京大学
        System.out.println(s2.name + "的学校：" + s2.school);  // 北京大学
        // 修改静态变量，所有对象都受影响
        Student.school = "清华大学";
        System.out.println(s1.name + "的学校：" + s1.school);  // 清华大学
    }
}

public class MathUtils {
    // 静态变量
    static final double PI = 3.14159265;
    // 静态方法
    public static int add(int a, int b) {
        return a + b;
    }
    public static double circleArea(double radius) {
        return PI * radius * radius;
    }
}
public class StaticMethodDemo {
    public static void main(String[] args) {
        // 通过类名调用静态方法
        int sum = MathUtils.add(10, 20);
        System.out.println("10 + 20 = " + sum);
        double area = MathUtils.circleArea(5);
        System.out.println("圆的面积：" + area);
    }
}

public class StudentManager {
    private String[] names;
    private int[] scores;
    private int count;
    private int capacity;
    public StudentManager(int capacity) {
        this.capacity = capacity;
        names = new String[capacity];
        scores = new int[capacity];
        count = 0;
    }
    public boolean addStudent(String name, int score) {
        if (count >= capacity) {
            System.out.println("学生数量已满");
            return false;
        }
        if (score < 0 || score > 100) {
            System.out.println("成绩无效");
            return false;
        }
        names[count] = name;
        scores[count] = score;
        count++;
        return true;
    }
    public void printAll() {
        System.out.println("=== 学生列表 ===");
        for (int i = 0; i < count; i++) {
            System.out.println(names[i] + "：" + scores[i] + "分");
        }
    }
    public double getAverage() {
        if (count == 0) return 0;
        int sum = 0;
        for (int i = 0; i < count; i++) {
            sum += scores[i];
        }
        return (double) sum / count;
    }
}