diff --git a/src/chapter4/Example01.java b/src/chapter4/Example01.java
new file mode 100644
index 0000000..1ec110b
--- /dev/null
+++ b/src/chapter4/Example01.java
@@ -0,0 +1,44 @@
+package chapter4;
+
+class Animal {
+ private String name;
+ private int age;
+
+ public String getName() {
+ return name;
+ }
+
+ public void setName(String name) {
+ this.name = name;
+ }
+
+ public int getAge() {
+ return age;
+ }
+
+ public void setAge(int age) {
+ this.age = age;
+ }
+}
+
+// 定义 Dog 类继承 Animal 类
+class Dog extends Animal {
+ private String color;
+
+ public String getColor() {
+ return color;
+ }
+
+ public void setColor(String color) {
+ this.color = color;
+ }
+}
+
+public class Example01 {
+ public static void main(String[] args) {
+ Dog dog = new Dog();
+ dog.setName("牧羊犬");
+ dog.setAge(3);
+ System.out.println("名称：" + dog.getName() + "，年龄：" + dog.getAge());
+ }
+}
diff --git a/src/chapter4/Example02.java b/src/chapter4/Example02.java
new file mode 100644
index 0000000..320744e
--- /dev/null
+++ b/src/chapter4/Example02.java
@@ -0,0 +1,5 @@
+package chapter4;
+
+
+public class Example02 {
+}
diff --git a/src/chapter4/Example11/Example11.java b/src/chapter4/Example11/Example11.java
new file mode 100644
index 0000000..f8cac74
--- /dev/null
+++ b/src/chapter4/Example11/Example11.java
@@ -0,0 +1,46 @@
+package chapter4.Example11;
+
+interface Animal {
+ int ID = 1; // 接口默认为常量添加 public static final
+ String NAME = "牧羊犬"; // 接口默认为常量添加 public static final
+
+ // 定义抽象方法shout()，接口默认添加 public abstract
+ void shout();
+
+ // 静态方法，默认添加 public
+ static int getID() {
+ return Animal.ID;
+ }
+
+ // 抽象方法
+ public void info();
+}
+
+interface Action {
+ public void eat();
+}
+
+class Dog implements Animal, Action {
+ public void eat() {
+ System.out.println("喜欢吃骨头");
+ }
+
+ // 重写Animal接口中的抽象方法shout()
+ public void shout() {
+ System.out.println("汪汪...");
+ }
+
+ public void info() {
+ System.out.println("名称：" + NAME);
+ }
+}
+
+public class Example11 {
+ public static void main(String[] args) {
+ System.out.println("编号：" + Animal.getID());
+ Dog dog = new Dog();
+ dog.info();
+ dog.shout();
+ dog.eat();
+ }
+}
diff --git a/src/chapter4/demo45/Circle.java b/src/chapter4/demo45/Circle.java
new file mode 100644
index 0000000..5269bc9
--- /dev/null
+++ b/src/chapter4/demo45/Circle.java
@@ -0,0 +1,27 @@
+package chapter4.demo45;
+
+/**
+ * 圆形类
+ * 必需实现 Shape 接口中的 getArea 和 getPerimeter 方法
+ */
+public class Circle implements Shape {
+ // 半径
+ private double radius = 0;
+ private final static double PI = 3.14;
+
+ // 有参构造
+ public Circle(double radius) {
+ this.radius = radius;
+ }
+
+ // 返回面积
+ public double getArea() {
+ return PI * radius * radius;
+ }
+
+ // 返回周长
+ public double getPerimeter() {
+ return 2 * PI * radius;
+ }
+
+}
diff --git a/src/chapter4/demo45/Main.java b/src/chapter4/demo45/Main.java
new file mode 100644
index 0000000..8946290
--- /dev/null
+++ b/src/chapter4/demo45/Main.java
@@ -0,0 +1,49 @@
+package chapter4.demo45;
+
+import java.util.Scanner;
+
+public class Main {
+ public static void main(String[] args) {
+ // 处理用户输入
+ Scanner sc = new Scanner(System.in);
+
+ while(true) {
+ // 打印菜单
+ ShapeCalculate.printMenu();
+ int select = sc.nextInt();
+ // 判断用户选项
+ switch (select) {
+ case 1: // 圆形
+ System.out.print("请输入圆形的半径：");
+ double radius = sc.nextDouble();
+ Shape circle = new Circle(radius);
+ ShapeCalculate.printArea(circle);
+ ShapeCalculate.printPerimeter(circle);
+ break;
+ case 2: // 长方形
+ System.out.print("请输入长方形的长和宽：");
+ double length = sc.nextDouble();
+ double width = sc.nextDouble();
+ Shape rectangle = new Rectangle(length, width);
+ ShapeCalculate.printArea(rectangle);
+ ShapeCalculate.printPerimeter(rectangle);
+ break;
+ default:
+ System.out.println("输入错误，请重新选择");
+ ShapeCalculate.printMenu();
+ break;
+ }
+ // 询问用户是否继续
+ System.out.println("继续计算？（Y / N）");
+ String answer = sc.next();
+ if ("N".equalsIgnoreCase(answer)) { // 无论大小写，都识别
+ break;
+ }
+ }
+ System.out.println("感谢您的使用，再见！");
+ sc.close();
+ }
+
+
+
+}
diff --git a/src/chapter4/demo45/Rectangle.java b/src/chapter4/demo45/Rectangle.java
new file mode 100644
index 0000000..55132af
--- /dev/null
+++ b/src/chapter4/demo45/Rectangle.java
@@ -0,0 +1,29 @@
+package chapter4.demo45;
+
+/**
+ * 长方形类
+ * 必需实现 Shape 接口中的 getArea 和 getPerimeter 方法
+ */
+
+public class Rectangle implements Shape {
+ // 长度
+ private double length = 0;
+ // 宽度
+ private double width = 0;
+
+ // 有参构造
+ public Rectangle(double length, double width) {
+ this.length = length;
+ this.width = width;
+ }
+
+ // 获取面积
+ public double getArea() {
+ return length * width;
+ }
+
+ // 获取周长
+ public double getPerimeter() {
+ return 2 * length + 2 * width;
+ }
+}
diff --git a/src/chapter4/demo45/Shape.java b/src/chapter4/demo45/Shape.java
new file mode 100644
index 0000000..b992fae
--- /dev/null
+++ b/src/chapter4/demo45/Shape.java
@@ -0,0 +1,15 @@
+package chapter4.demo45;
+
+/**
+ * 定义“图形”接口，只拥有抽象方法
+ * 后续的圆形和长方形都实现该接口，即圆形和长方形都需要实现 getArea 和 getPerimeter 方法
+ * 通过接口，可以制订“规范、规范”
+ */
+public interface Shape {
+ // 获取面积，省略 public abstract
+ double getArea();
+ // 获取周长，省略 public abstract
+ double getPerimeter();
+}
+
+
diff --git a/src/chapter4/demo45/ShapeCalculate.java b/src/chapter4/demo45/ShapeCalculate.java
new file mode 100644
index 0000000..434e53c
--- /dev/null
+++ b/src/chapter4/demo45/ShapeCalculate.java
@@ -0,0 +1,31 @@
+package chapter4.demo45;
+
+/**
+ * 图形计算器类
+ * 1. final 类：防止被继承
+ * 2. 私有构造函数（不可被实例化）
+ * 只有静态方法，不需要实例化，所有方法都可以通过类名调用
+ */
+public final class ShapeCalculate {
+ private ShapeCalculate() {
+ throw new AssertionError("不应该被实例化");
+ }
+
+ // 打印图形面积
+ public static void printArea(Shape shape) {
+ System.out.println("面积："+shape.getArea());
+ }
+
+ // 打印图形周长
+ public static void printPerimeter(Shape shape) {
+ System.out.println("周长："+shape.getPerimeter());
+ }
+
+ // 打印计算器菜单
+ public static void printMenu() {
+ System.out.println("==========图形计算器==========");
+ System.out.println("1.圆形");
+ System.out.println("2.长方形");
+ System.out.print("请输入序号选择功能：");
+ }
+}
diff --git a/src/chapter4/example07/Example07.java b/src/chapter4/example07/Example07.java
new file mode 100644
index 0000000..b723756
--- /dev/null
+++ b/src/chapter4/example07/Example07.java
@@ -0,0 +1,15 @@
+package chapter4.example07;
+
+final class Animal {
+ // 空
+}
+
+//class Dog extends Animal {
+//
+//}
+
+public class Example07 {
+ public static void main(String[] args) {
+// Dog dog = new Dog();
+ }
+}
diff --git a/src/chapter4/example10/Example10.java b/src/chapter4/example10/Example10.java
new file mode 100644
index 0000000..290b1ff
--- /dev/null
+++ b/src/chapter4/example10/Example10.java
@@ -0,0 +1,19 @@
+package chapter4.example10;
+
+abstract class Animal {
+ abstract void shout();
+
+}
+
+class Dog extends Animal {
+ void shout() {
+ System.out.println("汪汪...");
+ }
+}
+
+public class Example10 {
+ public static void main(String[] args) {
+ Animal dog = new Dog();
+ dog.shout();
+ }
+}