feat(class25): 添加单例模式示例代码

- 新增 A 类和 B 类作为单例模式的示例
- 更新 .gitignore 文件，忽略 META-INF 和 MANIFEST.MF 文件
- 在项目设置中添加 Lombok 注解支持
- 修改 Test 类，注释掉 SilverCard 相关代码
- 新增 Test 类测试单例模式

.gitignore

@@ -28,4 +28,7 @@ bin/
 .vscode/
 
 ### Mac OS ###
-.DS_Store
+.DS_Store
+
+META-INF/
+MANIFEST.MF

.idea/misc.xml

@@ -1,5 +1,10 @@
 <?xml version="1.0" encoding="UTF-8"?>
 <project version="4">
+  <component name="EntryPointsManager">
+    <writeAnnotations>
+      <writeAnnotation name="lombok.Getter" />
+    </writeAnnotations>
+  </component>
   <component name="ProjectRootManager" version="2" languageLevel="JDK_21" default="true" project-jdk-name="21" project-jdk-type="JavaSDK">
     <output url="file://$PROJECT_DIR$/out" />
   </component>

HM-JAVA.iml

@@ -4,6 +4,7 @@
     <exclude-output />
     <content url="file://$MODULE_DIR$">
       <sourceFolder url="file://$MODULE_DIR$/src" isTestSource="false" />
+      <excludeFolder url="file://$MODULE_DIR$/.idea/artifacts" />
     </content>
     <orderEntry type="inheritedJdk" />
     <orderEntry type="sourceFolder" forTests="false" />

src/class23/Test.java

@@ -8,8 +8,8 @@ public class Test {
         goldCard.deposit(1000);
         pay(goldCard);
 
-        SilverCard silverCard = new SilverCard("654321", "李四", 123456789, 5000);
-        pay(silverCard);
+//        SilverCard silverCard = new SilverCard("654321", "李四", 123456789, 5000);
+//        pay(silverCard);
     }
     public static void pay(Card c){
         System.out.println("请刷卡，请输入您的消费金额：");

src/class25/A.java

@@ -0,0 +1,11 @@
+package class25;
+
+import lombok.Getter;
+
+public class A {
+    //单例类
+    @Getter
+    private static final A a = new A();
+    private A(){}
+
+}

src/class25/B.java

@@ -0,0 +1,13 @@
+package class25;
+
+public class B {
+    private static B b;
+    private B() {
+    }
+    public static B getInstance() {
+        if (b == null) {
+            b = new B();
+        }
+        return b;
+    }
+}

src/class25/Test.java

@@ -0,0 +1,19 @@
+package class25;
+
+public class Test {
+    public static void main(String[] args) {
+        A a = A.getA();
+        A a2 = A.getA();
+        System.out.println(a==a2);
+        System.out.println(a.hashCode());
+        System.out.println(a2.hashCode());
+        System.out.println("================");
+        B b = B.getInstance();
+        B b1 = B.getInstance();
+        System.out.println(b==b1);
+        System.out.println(b.hashCode());
+        System.out.println(b1.hashCode());
+
+
+    }
+}