feat: add java 20 demo

niumoo · niumoo · commit 15952a5811b1 · 2023-05-05T11:55:52.000+08:00
diff --git a/core-java-modules/core-java-20/src/JEP433SwitchTest.java b/core-java-modules/core-java-20/src/JEP433SwitchTest.java
@@ -0,0 +1,56 @@
+/**
+ * @author niulang
+ */
+public class JEP433SwitchTest {
+    public static void main(String[] args) {
+        Object obj = 123;
+        System.out.println(matchOld(obj)); // 是个数字
+        System.out.println(matchNew(obj)); // 是个数字
+        obj = "wdbyte.com";
+        System.out.println(matchOld(obj)); // 是个字符串，长度大于2
+        System.out.println(matchNew(obj)); // 是个字符串，长度大于2
+    }
+
+    /**
+     * 老代码
+     *
+     * @param obj
+     * @return
+     */
+    public static String matchOld(Object obj) {
+        if (obj == null) {
+            return "数据为空";
+        }
+        if (obj instanceof String) {
+            String s = obj.toString();
+            if (s.length() > 2) {
+                return "是个字符串，长度大于2";
+            }
+            if (s.length() <= 2) {
+                return "是个字符串，长度小于等于2";
+            }
+        }
+        if (obj instanceof Integer) {
+            return "是个数字";
+        }
+        throw new IllegalStateException("未知数据：" + obj);
+    }
+
+    /**
+     * 新代码
+     *
+     * @param obj
+     * @return
+     */
+    public static String matchNew(Object obj) {
+        String res = switch (obj) {
+            case null -> "数据为空";
+            case String s when s.length() > 2 -> "是个字符串，长度大于2";
+            case String s when s.length() <= 2 -> "是个字符串，长度小于等于于2";
+            case Integer i -> "是个数字";
+            default -> throw new IllegalStateException("未知数据：" + obj);
+        };
+        return res;
+    }
+
+}
diff --git a/core-java-modules/core-java-20/src/Jep429ScopedValueTest.java b/core-java-modules/core-java-20/src/Jep429ScopedValueTest.java
@@ -0,0 +1,28 @@
+import jdk.incubator.concurrent.ScopedValue;
+
+/**
+ * --add-modules jdk.incubator.concurrent
+ *
+ * @date 2023/05/04
+ */
+public class Jep429ScopedValueTest {
+    final static ScopedValue<String> SCOPED_VALUE = ScopedValue.newInstance();
+
+    public static void main(String[] args) {
+        // 创建线程
+        Thread thread1 = new Thread(Jep429ScopedValueTest::handle);
+        Thread thread2 = new Thread(Jep429ScopedValueTest::handle);
+        String str = "hello wdbyte";
+        // 传入线程里使用的字符串信息
+        ScopedValue.where(SCOPED_VALUE, str).run(thread1);
+        ScopedValue.where(SCOPED_VALUE, str).run(thread2);
+        // 执行完毕自动清空，这里获取不到了。
+        System.out.println(SCOPED_VALUE.orElse("没有信息"));
+    }
+
+    public static void handle() {
+        String result = SCOPED_VALUE.get();
+        System.out.println(result);
+    }
+
+}
diff --git a/core-java-modules/core-java-20/src/Jep432RecordAndInstance.java b/core-java-modules/core-java-20/src/Jep432RecordAndInstance.java
@@ -0,0 +1,22 @@
+/**
+ * @author niulang
+ */
+public class Jep432RecordAndInstance {
+    public static void main(String[] args) {
+        ColoredPoint coloredPoint1 = new ColoredPoint(new Point(0, 0), Color.RED);
+        ColoredPoint coloredPoint2 = new ColoredPoint(new Point(1, 1), Color.GREEN);
+        Rectangle rectangle = new Rectangle(coloredPoint1, coloredPoint2);
+        printUpperLeftColoredPoint(rectangle);
+    }
+
+    static void printUpperLeftColoredPoint(Rectangle r) {
+        if (r instanceof Rectangle(ColoredPoint ul, ColoredPoint lr)) {
+            System.out.println(ul.c());
+        }
+    }
+}
+
+record Point(int x, int y) {}
+enum Color { RED, GREEN, BLUE }
+record ColoredPoint(Point p, Color c) {}
+record Rectangle(ColoredPoint upperLeft, ColoredPoint lowerRight) {}
diff --git a/core-java-modules/core-java-20/src/RecordTest.java b/core-java-modules/core-java-20/src/RecordTest.java
@@ -0,0 +1,14 @@
+/**
+ * @author niulang
+ * @date 2023/05/04
+ */
+public class RecordTest {
+    public static void main(String[] args) {
+        Dog dog = new Dog("name", 1);
+        System.out.println(dog.name());
+        System.out.println(dog.age());
+    }
+}
+
+record Dog(String name, Integer age) {
+}
