Java 异常处理 try-catch-resourses

//JDK7的改进方案
private static void method3() {
try(FileReader fr = new FileReader("fr.txt");
FileWriter fw = new FileWriter("fw.txt");){
char[] chs = new char[1024];
int len;
while ((len = fr.read()) != -1) {
fw.write(chs, 0, len);
}
} catch (IOException e) {
e.printStackTrace();
}
}

//JDK9的改进方案
private static void method4() throws IOException {
FileReader fr = new FileReader("fr.txt");
FileWriter fw = new FileWriter("fw.txt");
try(fr;fw){
char[] chs = new char[1024];
int len;
while ((len = fr.read()) != -1) {
fw.write(chs, 0, len);
}
} catch (IOException e) {
e.printStackTrace();
}
}