update:demo2

com/study/demo2/Account.java

@@ -0,0 +1,36 @@
+package com.study.demo2;
+
+public class Account {
+    private String accountId;
+    private String owner;
+    private double balance;
+
+    public Account(String accountId, String owner, double balance) {
+        this.accountId = accountId;
+        this.owner = owner;
+        this.balance = balance;
+    }
+
+    public void deposit(double amount) {
+        if (amount > 0) {
+            balance += amount;
+        }
+    }
+
+    public void withdraw(double amount) {
+        if (amount > 0 && amount <= balance) {
+            balance -= amount;
+        }
+    }
+
+    public void transfer(Account target, double amount) {
+        if (amount > 0 && amount <= balance) {
+            this.balance -= amount;
+            target.balance += amount;
+        }
+    }
+
+    public double getBalance() {
+        return balance;
+    }
+}

com/study/demo2/Account_Main.java

@@ -0,0 +1,15 @@
+package com.study.demo2;
+
+public class Main {
+    public static void main(String[] args) {
+        Account acc1 = new Account("A001", "张三", 1000);
+        Account acc2 = new Account("A002", "李四", 500);
+        
+        acc1.deposit(200);
+        acc1.withdraw(100);
+        acc1.transfer(acc2, 300);
+        
+        System.out.println("账户1余额:" + acc1.getBalance());
+        System.out.println("账户2余额:" + acc2.getBalance());
+    }
+}

com/study/demo2/Animal.java

@@ -0,0 +1,44 @@
+package com.study.demo2;
+
+public abstract class Animal {
+    protected String name;
+
+    public Animal(String name) {
+        this.name = name;
+    }
+
+    public abstract void makeSound();
+    public abstract void move();
+}
+
+class Dog extends Animal {
+    public Dog(String name) {
+        super(name);
+    }
+
+    @Override
+    public void makeSound() {
+        System.out.println(name + " 汪汪叫");
+    }
+
+    @Override
+    public void move() {
+        System.out.println(name + " 跑动");
+    }
+}
+
+class Bird extends Animal {
+    public Bird(String name) {
+        super(name);
+    }
+
+    @Override
+    public void makeSound() {
+        System.out.println(name + " 叽叽喳喳");
+    }
+
+    @Override
+    public void move() {
+        System.out.println(name + " 飞翔");
+    }
+}

com/study/demo2/Animal_Main.java

@@ -0,0 +1,12 @@
+package com.study.demo2;
+
+public class Main {
+    public static void main(String[] args) {
+        Animal dog = new Dog("Buddy");
+        Animal bird = new Bird("Tweety");
+        dog.makeSound();
+        dog.move();
+        bird.makeSound();
+        bird.move();
+    }
+}

com/study/demo2/Rectangle.java

@@ -0,0 +1,37 @@
+package com.study.demo2;
+
+public class Rectangle {
+    private double width = 1.0;
+    private double height = 1.0;
+
+    public Rectangle() {}
+
+    public Rectangle(double width, double height) {
+        this.width = width;
+        this.height = height;
+    }
+
+    public double getArea() {
+        return width * height;
+    }
+
+    public double getPerimeter() {
+        return 2 * (width + height);
+    }
+
+    public double getWidth() {
+        return width;
+    }
+
+    public void setWidth(double width) {
+        this.width = width;
+    }
+
+    public double getHeight() {
+        return height;
+    }
+
+    public void setHeight(double height) {
+        this.height = height;
+    }
+}

com/study/demo2/Rectangle_Main.java

@@ -0,0 +1,18 @@
+package com.study.demo2;
+
+public class Main {
+    public static void main(String[] args) {
+        Rectangle rect1 = new Rectangle(5.0, 3.0);
+        System.out.println("面积:" + rect1.getArea());
+        System.out.println("周长:" + rect1.getPerimeter());
+        
+        Rectangle rect2 = new Rectangle();
+        System.out.println("默认面积:" + rect2.getArea());
+        System.out.println("默认周长:" + rect2.getPerimeter());
+        
+        rect2.setWidth(2.5);
+        rect2.setHeight(4.0);
+        System.out.println("修改后面积:" + rect2.getArea());
+        System.out.println("修改后周长:" + rect2.getPerimeter());
+    }
+}

com/study/demo2/Student.java

@@ -0,0 +1,40 @@
+package com.study.demo2;
+
+public class Student {
+    private String id;
+    private String name;
+    private int[] score = new int[10];
+
+    public Student(String id, String name, int[] scores) {
+        this.id = id;
+        this.name = name;
+        if (scores.length == 10) {
+            this.score = scores;
+        }
+    }
+
+    public double getAverage() {
+        int sum = 0;
+        for (int s : score) {
+            sum += s;
+        }
+        return (double) Math.round((sum / 10.0) * 100) / 100;
+    }
+
+    public int getMaxScore() {
+        int max = score[0];
+        for (int s : score) {
+            if (s > max) max = s;
+        }
+        return max;
+    }
+
+    public char getGrade() {
+        double avg = getAverage();
+        if (avg >= 90) return 'A';
+        else if (avg >= 80) return 'B';
+        else if (avg >= 70) return 'C';
+        else if (avg >= 60) return 'D';
+        else return 'E';
+    }
+}

com/study/demo2/Student_Main.java

@@ -0,0 +1,12 @@
+package com.study.demo2;
+
+public class Main {
+    public static void main(String[] args) {
+        int[] scores = {85, 90, 78, 92, 88, 76, 95, 89, 79, 94};
+        Student student = new Student("5001", "张三", scores);
+        
+        System.out.println("平均分: " + student.getAverage());
+        System.out.println("最高分: " + student.getMaxScore());
+        System.out.println("等级: " + student.getGrade());
+    }
+}