提交单例模式代码

Author: sgr

singleton/src/main/java/os/dt/design/patterns/singleton/EnumPresident.java

@@ -0,0 +1,16 @@
+package os.dt.design.patterns.singleton;
+
+/**
+ * 枚举式
+ * 不仅线程安全，还可以反序列化
+ * （有点别扭）
+ * Created by songgr on 2019/10/17.
+ */
+public enum EnumPresident {
+ INSTANCE;
+
+ public void run(){
+ System.out.println("EnumPresident run ...");
+ }
+
+}

singleton/src/main/java/os/dt/design/patterns/singleton/HungryPresident.java

@@ -2,6 +2,10 @@
 
 /**
  * 饿汉式写法
+ * （简单实用，比较推荐）
+ * 类加载到内存后，只实例化一个实例，JVM保证线程安全的
+ * 缺点：实例不管后续有没有使用，类加载实就完成实例化 （但是话说如果这个类不用的话，你也没必要加载呀）
+ *
  * Created by songgr on 2019/10/17.
  */
 public class HungryPresident {

singleton/src/main/java/os/dt/design/patterns/singleton/InitializingOnDemandHolderPresident.java

@@ -0,0 +1,25 @@
+package os.dt.design.patterns.singleton;
+
+/**
+ * 静态内部类方式
+ * JVM保持单例 （JVM加载类只加载一次）
+ * 加载外部类时不会加载内部类，这样可以实现懒加载
+ * Created by songgr on 2019/10/17.
+ */
+public class InitializingOnDemandHolderPresident {
+
+ private InitializingOnDemandHolderPresident(){
+
+ }
+
+ // 可以做到延迟加载
+ private static class HelperHolder {
+ private static final InitializingOnDemandHolderPresident INSTANCE =
+ new InitializingOnDemandHolderPresident();
+ }
+
+ public static InitializingOnDemandHolderPresident getInstance() {
+ return HelperHolder.INSTANCE;
+ }
+
+}

singleton/src/main/java/os/dt/design/patterns/singleton/LazyLoadPresident.java

@@ -0,0 +1,25 @@
+package os.dt.design.patterns.singleton;
+
+/**
+ * 懒汉式写法
+ * 虽然不用在类加载是实例化做到了按需去初始化，但实例线程不安全
+ * Created by songgr on 2019/10/17.
+ */
+public class LazyLoadPresident {
+
+ private static LazyLoadPresident INSTANCE;
+
+ private LazyLoadPresident() {
+
+ }
+
+ public static LazyLoadPresident getInstance() {
+
+ if (INSTANCE == null) {
+ System.out.println("getInstance");
+ INSTANCE = new LazyLoadPresident();
+ }
+
+ return INSTANCE;
+ }
+}

singleton/src/main/java/os/dt/design/patterns/singleton/ThreadSafeDoubleCheckPresident.java

@@ -0,0 +1,29 @@
+package os.dt.design.patterns.singleton;
+
+/**
+ * 线程安全的双重检查方式
+ * Created by songgr on 2019/10/17.
+ */
+public class ThreadSafeDoubleCheckPresident {
+
+ // 必须加volatile
+ private static volatile ThreadSafeDoubleCheckPresident INSTANCE;
+
+ private ThreadSafeDoubleCheckPresident() {
+
+ }
+
+ public static ThreadSafeDoubleCheckPresident getInstance() {
+ if (INSTANCE == null) { // 这层判断是有必要的 大多数情况下INSTANCE不为null直接返回了，减少了加锁的操作
+ System.out.println("getInstance");
+ synchronized (ThreadSafeDoubleCheckPresident.class) {
+ if (INSTANCE == null) {
+ INSTANCE = new ThreadSafeDoubleCheckPresident();
+ }
+ }
+ }
+
+ return INSTANCE;
+ }
+
+}

singleton/src/main/java/os/dt/design/patterns/singleton/ThreadSafeLazyLoadPresident.java

@@ -0,0 +1,23 @@
+package os.dt.design.patterns.singleton;
+
+/**
+ * 线程安全的懒汉写法
+ * 缺点每次获取对象都得加锁，效率低下
+ * Created by songgr on 2019/10/17.
+ */
+public class ThreadSafeLazyLoadPresident {
+
+ private static ThreadSafeLazyLoadPresident INSTANCE;
+
+ private ThreadSafeLazyLoadPresident() {
+
+ }
+
+ public static synchronized ThreadSafeLazyLoadPresident getInstance() {
+ if (INSTANCE == null) {
+ System.out.println("getInstance");
+ INSTANCE = new ThreadSafeLazyLoadPresident();
+ }
+ return INSTANCE;
+ }
+}

singleton/src/test/java/os/dt/design/patterns/singleton/UnitTest.java

@@ -9,7 +9,6 @@
 import java.util.concurrent.ExecutorService;
 import java.util.concurrent.Executors;
 import java.util.concurrent.TimeUnit;
-import java.util.function.Function;
 import java.util.function.Supplier;
 
 /**
@@ -32,6 +31,7 @@ public CreateObj(Supplier function) {
  public void run() {
  System.out.println(Thread.currentThread().getName() + ": I get a obj.");
  Object obj = function.get();
+ System.out.println(obj.hashCode());
  objs.add(obj);
  }
  }
@@ -59,11 +59,89 @@ public void hungryPresident() throws InterruptedException {
 
  }
 
+ @Test
+ public void lazyLoadPresident() throws InterruptedException {
+ ExecutorService fixedThreadPool = Executors.newFixedThreadPool(4);
+
+ fixedThreadPool.submit(new CreateObj(() -> LazyLoadPresident.getInstance()));
+ fixedThreadPool.submit(new CreateObj(() -> LazyLoadPresident.getInstance()));
+ fixedThreadPool.submit(new CreateObj(() -> LazyLoadPresident.getInstance()));
+ fixedThreadPool.submit(new CreateObj(() -> LazyLoadPresident.getInstance()));
+
+ fixedThreadPool.awaitTermination(4, TimeUnit.SECONDS);
+
+ }
+
+ @Test
+ public void threadSafelazyLoadPresident() throws InterruptedException {
+ ExecutorService fixedThreadPool = Executors.newFixedThreadPool(4);
+
+ fixedThreadPool.submit(new CreateObj(() -> ThreadSafeLazyLoadPresident.getInstance()));
+ fixedThreadPool.submit(new CreateObj(() -> ThreadSafeLazyLoadPresident.getInstance()));
+ fixedThreadPool.submit(new CreateObj(() -> ThreadSafeLazyLoadPresident.getInstance()));
+ fixedThreadPool.submit(new CreateObj(() -> ThreadSafeLazyLoadPresident.getInstance()));
+
+ fixedThreadPool.awaitTermination(4, TimeUnit.SECONDS);
+
+ }
+
+ @Test
+ public void threadSafeDoubleCheckPredident() throws InterruptedException {
+ ExecutorService fixedThreadPool = Executors.newFixedThreadPool(4);
+
+ fixedThreadPool.submit(new CreateObj(() -> ThreadSafeDoubleCheckPresident.getInstance()));
+ fixedThreadPool.submit(new CreateObj(() -> ThreadSafeDoubleCheckPresident.getInstance()));
+ fixedThreadPool.submit(new CreateObj(() -> ThreadSafeDoubleCheckPresident.getInstance()));
+ fixedThreadPool.submit(new CreateObj(() -> ThreadSafeDoubleCheckPresident.getInstance()));
+
+ fixedThreadPool.awaitTermination(4, TimeUnit.SECONDS);
+
+ }
+
+
+ @Test
+ public void initializingOnDemandHolderPresident() throws InterruptedException {
+ ExecutorService fixedThreadPool = Executors.newFixedThreadPool(4);
+
+ fixedThreadPool.submit(new CreateObj(() -> InitializingOnDemandHolderPresident.getInstance()));
+ fixedThreadPool.submit(new CreateObj(() -> InitializingOnDemandHolderPresident.getInstance()));
+ fixedThreadPool.submit(new CreateObj(() -> InitializingOnDemandHolderPresident.getInstance()));
+ fixedThreadPool.submit(new CreateObj(() -> InitializingOnDemandHolderPresident.getInstance()));
+
+ fixedThreadPool.awaitTermination(4, TimeUnit.SECONDS);
+
+ }
+
+
+ @Test
+ public void enumPresident() throws InterruptedException {
+ ExecutorService fixedThreadPool = Executors.newFixedThreadPool(4);
+
+ EnumPresident.INSTANCE.run();
+
+ fixedThreadPool.submit(new CreateObj(() -> EnumPresident.INSTANCE));
+ fixedThreadPool.submit(new CreateObj(() -> EnumPresident.INSTANCE));
+ fixedThreadPool.submit(new CreateObj(() -> EnumPresident.INSTANCE));
+ fixedThreadPool.submit(new CreateObj(() -> EnumPresident.INSTANCE));
+
+ fixedThreadPool.awaitTermination(4, TimeUnit.SECONDS);
+
+ }
+
+
+
+
  @After
  public void check() {
  assert objs.size() > 1;
- objs.stream().reduce((a,b) -> a == b);
- objs.stream().forEach(a -> System.out.println(a.getClass()));
+
+ for (int i=0; i<objs.size()-1; i++){
+ for (int j=i+1; j<objs.size(); j++){
+ assert objs.get(i) == objs.get(j);
+ }
+ }
+
+ objs.stream().forEach(a -> System.out.println(a.getClass() + " " + a.hashCode()));
  }