int i = 5;  long j = 10;    i += j; //正常  i = i+j; //報錯，Incompatible types.

A compound assignment expression of the form E1 op= E2 is equivalent to E1 = (T) ((E1) op (E2)), where T is the type of E1, except that E1 is evaluated only once.

byte b = 1;  b += 1;

ThreadLocalRandom.current().nextInt();

protected int next(int bits) {      long oldseed, nextseed;      AtomicLong seed = this.seed;      do {          oldseed = seed.get();          nextseed = (oldseed * multiplier + addend) & mask;      } while (!seed.compareAndSet(oldseed, nextseed));      return (int)(nextseed >>> (48 - bits));  }

final long nextSeed() {      Thread t; long r; // read and update per-thread seed      UNSAFE.putLong(t = Thread.currentThread(), SEED,                     r = UNSAFE.getLong(t, SEED) + GAMMA);      return r;  }

String str = "測試";  InputStream inputStream = new ByteArrayInputStream(str.getBytes());

/** 1. 使用 ByteArrayOutputStream 循環讀取 */  BufferedInputStream bis = new BufferedInputStream(inputStream);  ByteArrayOutputStream buf = new ByteArrayOutputStream();  int tmpRes = bis.read();  while(tmpRes != -1) {      buf.write((byte) tmpRes);      tmpRes = bis.read();  }  System.out.println(buf.toString());

/** 2. 使用 InputStreamReader 批量讀取 */  final char[] buffer = new char[1024];  final StringBuilder out = new StringBuilder();  Reader in = new InputStreamReader(inputStream);  for (; ; ) {      int rsz = in.read(buffer, 0, buffer.length);      if (rsz < 0) {          break;      }      out.append(buffer, 0, rsz);  }  System.out.println(out.toString());

/** 3. 使用 JDK Scanner */  Scanner s = new Scanner(inputStream).useDelimiter("\A");  String result = s.hasNext() ? s.next() : "";  System.out.println(result);

/** 4. 使用 Java 8 Stream API */  result = new BufferedReader(new InputStreamReader(inputStream))          .lines().collect(Collectors.joining("n"));  System.out.println(result);

/** 5. 使用 IOUtils StringWriter */  StringWriter stringWriter = new StringWriter();  IOUtils.copy(inputStream, stringWriter);  System.out.println(stringWriter.toString());

/** 6. 使用 IOUtils.toString 一步到位 */  System.out.println(IOUtils.toString(inputStream));

public final class ClassLoaderLeakExample {      static volatile boolean running = true;      /**       * 1. main 函數，邏輯比較簡單只是創建一個 LongRunningThread 執行緒，並接受停止的指令       */      public static void main(String[] args) throws Exception {          Thread thread = new LongRunningThread();          try {              thread.start();              System.out.println("Running, press any key to stop.");              System.in.read();          } finally {              running = false;              thread.join();          }      }        /**       * 2. 定義 LongRunningThread 執行緒，該執行緒做的事情比較簡單，每隔 100ms 調用 loadAndDiscard 方法       */      static final class LongRunningThread extends Thread {          @Override public void run() {              while(running) {                  try {                      loadAndDiscard();                  } catch (Throwable ex) {                      ex.printStackTrace();                  }                  try {                      Thread.sleep(100);                  } catch (InterruptedException ex) {                      System.out.println("Caught InterruptedException, shutting down.");                      running = false;                  }              }          }      }        /**       * 3. 定義一個 class loader - ChildOnlyClassLoader，它在我們的例子中至關重要。       * ChildOnlyClassLoader 專門用來裝載 LoadedInChildClassLoader 類，       * 邏輯比較簡單，讀取 LoadedInChildClassLoader 類的 .class 文件，返回類對象。       */      static final class ChildOnlyClassLoader extends ClassLoader {          ChildOnlyClassLoader() {              super(ClassLoaderLeakExample.class.getClassLoader());          }            @Override protected Class<?> loadClass(String name, boolean resolve)                  throws ClassNotFoundException {              if (!LoadedInChildClassLoader.class.getName().equals(name)) {                  return super.loadClass(name, resolve);              }              try {                  Path path = Paths.get(LoadedInChildClassLoader.class.getName()                          + ".class");                  byte[] classBytes = Files.readAllBytes(path);                  Class<?> c = defineClass(name, classBytes, 0, classBytes.length);                  if (resolve) {                      resolveClass(c);                  }                  return c;              } catch (IOException ex) {                  throw new ClassNotFoundException("Could not load " + name, ex);              }          }      }        /**       * 4. 編寫 loadAndDiscard 方法的程式碼，也就是在 LongRunningThread 執行緒中被調用的方法。       * 該方法創建 ChildOnlyClassLoader 對象，用來裝載 LoadedInChildClassLoader 類，將結果賦值給 childClass 變數，       * childClass 調用 newInstance 方法來創建 LoadedInChildClassLoader 對象。       * 每次調用 loadAndDiscard 方法，都會載入一次 LoadedInChildClassLoader 類並創建其對象。       */      static void loadAndDiscard() throws Exception {          ClassLoader childClassLoader = new ChildOnlyClassLoader();          Class<?> childClass = Class.forName(                  LoadedInChildClassLoader.class.getName(), true, childClassLoader);          childClass.newInstance();      }        /**       * 5. 定義 LoadedInChildClassLoader  類       * 該類中定義了一個 moreBytesToLeak 位元組數組，初始大小比較大是為了儘快模擬出記憶體泄漏的結果。       * 在類的構造方法調用 threadLocal 的 set 方法存儲對象本身的引用。       */      public static final class LoadedInChildClassLoader {          static final byte[] moreBytesToLeak = new byte[1024 * 1024 * 10];            private static final ThreadLocal<LoadedInChildClassLoader> threadLocal                  = new ThreadLocal<>();            public LoadedInChildClassLoader() {              threadLocal.set(this);          }      }  }

javac ClassLoaderLeakExample.java  java -cp . ClassLoaderLeakExample

Class<?> childClass = Class.forName(                  LoadedInChildClassLoader.class.getName(), true, childClassLoader);  //改為：  Class<?> childClass = Class.forName(                  LoadedInChildClassLoader.class.getName());