`IntelliJ IDEA`会提示
'try' can use automatic resource management。
从` Java 7 build 105`版本开始，`Java 7`的编译器和运行环境支持新的`try-with-resources`语句，称为`ARM` 块(`Automatic Resource Management`) ，自动资源管理。
新的语句支持包括流以及任何可关闭的资源。
public static void filyCopy(File one,File two){
FileInputStream fileInput = null;
FileOutputStream fileOutput = null;
try {
fileInput = new FileInputStream(one);
fileOutput = new FileOutputStream(two);
byte[] b = new byte[1024];
int len = 0;
while((len = fileInput.read(b)) != -1){
fileOutput.write(b, 0, len);
}
} catch (Exception e) {
e.printStackTrace();
} finally {//释放资源
try {
if(fileInput != null){
fileInput.close();
}
if(fileOutput != null){
fileOutput.close();
}
} catch (Exception e2) {
e2.printStackTrace();
}
}
}
使用`try-with-resources`语句来简化代码如下：
public static void filyCopy2(File one,File two){
try (FileInputStream fileInput = new FileInputStream(one);
FileOutputStream fileOutput = new FileOutputStream(two);){
byte[] b = new byte[1024];
int len = 0;
while((len = fileInput.read(b)) != -1){
fileOutput.write(b, 0, len);
}
} catch (Exception e) {
e.printStackTrace();
}
}
在这个例子中，数据流会在`try`执行完毕后自动被关闭，前提是，这些可关闭的资源必须实现`java.lang.AutoCloseable`接口。
注：目前`java.lang.AutoCloseable`接口的子接口或实现类如下：
所有已经子接口:
AsynchronousByteChannel, AsynchronousChannel, BaseStream, ByteChannel, CachedRowSet, CallableStatement, Channel, Clip, Closeable, Connection, DataLine, DirectoryStream, DoubleStream, FilteredRowSet, GatheringByteChannel, ImageInputStream, ImageOutputStream, InterruptibleChannel, JavaFileManager, JdbcRowSet, JMXConnector, JoinRowSet, Line, LongStream, MidiDevice, MidiDeviceReceiver, MidiDeviceTransmitter, Mixer, MulticastChannel, NetworkChannel, ObjectInput, ObjectOutput, Port, PreparedStatement, ReadableByteChannel, Receiver, RMIConnection, RowSet, ScatteringByteChannel, SecureDirectoryStream, SeekableByteChannel, Sequencer, SourceDataLine, StandardJavaFileManager, Statement, Stream, SyncResolver, Synthesizer, TargetDataLine, Transmitter, WatchService, WebRowSet, WritableByteChannel
所有已知实现类：
AbstractInterruptibleChannel, AbstractSelectableChannel, AbstractSelector, AsynchronousFileChannel, AsynchronousServerSocketChannel, AsynchronousSocketChannel, AudioInputStream, BufferedInputStream, BufferedOutputStream, BufferedReader, BufferedWriter, ByteArrayInputStream, ByteArrayOutputStream, CharArrayReader, CharArrayWriter, CheckedInputStream, CheckedOutputStream, CipherInputStream, CipherOutputStream, DatagramChannel, DatagramSocket, DataInputStream, DataOutputStream, DeflaterInputStream, DeflaterOutputStream, DigestInputStream, DigestOutputStream, FileCacheImageInputStream, FileCacheImageOutputStream, FileChannel, FileImageInputStream, FileImageOutputStream, FileInputStream, FileLock, FileOutputStream, FileReader, FileSystem, FileWriter, FilterInputStream, FilterOutputStream, FilterReader, FilterWriter, Formatter, ForwardingJavaFileManager, GZIPInputStream, GZIPOutputStream, ImageInputStreamImpl, ImageOutputStreamImpl, InflaterInputStream, InflaterOutputStream, InputStream, InputStream, InputStream, InputStreamReader, JarFile, JarInputStream, JarOutputStream, LineNumberInputStream, LineNumberReader, LogStream, MemoryCacheImageInputStream, MemoryCacheImageOutputStream, MLet, MulticastSocket, ObjectInputStream, ObjectOutputStream, OutputStream, OutputStream, OutputStream, OutputStreamWriter, Pipe.SinkChannel, Pipe.SourceChannel, PipedInputStream, PipedOutputStream, PipedReader, PipedWriter, PrintStream, PrintWriter, PrivateMLet, ProgressMonitorInputStream, PushbackInputStream, PushbackReader, RandomAccessFile, Reader, RMIConnectionImpl, RMIConnectionImpl_Stub, RMIConnector, RMIIIOPServerImpl, RMIJRMPServerImpl, RMIServerImpl, Scanner, SelectableChannel, Selector, ServerSocket, ServerSocketChannel, Socket, SocketChannel, SSLServerSocket, SSLSocket, StringBufferInputStream, StringReader,StringWriter,URLClassLoader, Writer, XMLDecoder, XMLEncoder, ZipFile,ZipInputStream, ZipOutputStream
对于`Android`用户来说，只有编译工程的 `minSdkVersion`大于` 19`(`Android 4.4`)的时候才能生效。
try-with-resources is only supported if your minSdkVersion is set to 19 or higher.