try(){}的简单理解

以前使用try catch-finally都是捕获异常,然后流关闭等等,代码总是这样的:好比往FileOutputStream写东西:

@Test
  public void test2() throws IOException {
    File file = new File("E://test");
    if (!file.exists()) {
      file.createNewFile();
    }
    FileOutputStream fileOutputStream = new FileOutputStream(file);
    try {
      System.out.println("do something...");
      fileOutputStream.write("aaa".getBytes());
      fileOutputStream.flush();
    } catch (Exception e) {
      System.out.println("do ...");
    } finally {
      fileOutputStream.close();
    }
  }

这样写很难受,可以进行优化,将FileOutputStream fileOutputStream = new FileOutputStream(file)放到try()里面,也可以放多个,

  @Test
  public void test2() throws IOException {
    File file = new File("E://test");
    if (!file.exists()) {
      file.createNewFile();
    }
   
    try( FileOutputStream fileOutputStream = new FileOutputStream(file);) {
      System.out.println("do something...");
      fileOutputStream.write("aaa".getBytes());
      fileOutputStream.flush();
    } catch (Exception e) {
      System.out.println("do ...");
    } 
  }

try()里每个声明的变量类型都必须是Closeable的子类,就一个close方法;相当于系统自动将关闭操作放到了finally里面而不需要我们自己写了,很nice;