자원이 둘 이상이면 try-finally 방식은 너무 지저분하다.

//기본 try-finally문
static void copy(String src, String dst) throws IOException{
InputStream in = new FileInputStream(src);
try{
	OutputStream out = new FileOutputStream(dst);
	try{
		...
	} finally{
		out.close();
	}
}

//try-with-resources 적용
static void copy(String src, String dst) throws IOException{
try(InputStream in = new FileInputStream(src);
	OutputStream out = new FileOutputStream(dst)){
	...
	}