try with resource, AutoCloseable

class implements AutoCloseableがtry with resourceできる
BufferedReadearなど。
try blockの最後でclose()が呼ばれる
class implements AutoCloseableがnullの場合はNullpointerは発生しない。closeもしない
記述した順番と逆順でclose

class Sample implements Closeable {
    String msg;
    Sample(String msg) {
        this.msg = msg;
    }
    @Override
    public void close() {
        System.out.println(this.msg + " close");
    }
    void method() {
        System.out.println(this.msg + " method");
    }
}
public class Outer {
    public static void main(String args[]) {
        Sample s = new Sample("s");
        Sample s1 = new Sample("s1");
        Sample s3 = new Sample("s3");
        Sample s2 = null;
        try (s;s1;s2;s3) {
            method(s);
            method(s2);
        }
    }
    static void method(Sample s) {
        if(s!=null)  s.method();
    }
}

s method
s3 close
s1 close
s close

try block, closeでexception occurの場合、
try block sideのexceptionが表面的なexception
close sideのexceptionは getSuppressed()で取得

class Sample implements Closeable {
    String msg;
    Sample(String msg) {
        this.msg = msg;
    }
    @Override
    public void close() {
        System.out.println(this.msg + " close");
        throw new RuntimeException();
    }
    void method() {
        System.out.println(this.msg + " method");
    }
}
public class Outer {
    public static void main(String args[]) {
        try (Sample s = new Sample("s")) {
            System.out.println(" try");
            throw new Exception();
        } catch (Exception ex) {
            System.out.println(ex);
            Throwable[] ts = ex.getSuppressed();
            for(Throwable t:ts) {
                System.out.println(t);
            }
            System.out.println(" catch");
        } finally {
            System.out.println(" finally");
        }
    }
}

 try
s close
java.lang.Exception
java.lang.RuntimeException
 catch
 finally