Java异常基础

public class Test {
	public static void main(String[] args) {
		File f = new File("file.txt");
		FileInputStream input = new FileInputStream(f);
	}

}

    上面的代码编译器会报错，我们看下FileInputStream的源码，其中有：

public FileInputStream(File file) throws FileNotFoundException {
		String name = (file != null ? file.getPath() : null);
		SecurityManager security = System.getSecurityManager();
		if (security != null) {
			security.checkRead(name);
		}
		if (name == null) {
			throw new NullPointerException();
		}
		fd = new FileDescriptor();
		fd.incrementAndGetUseCount();
		open(name);
	}

    可以看到FileInputStream的构造方法指出，它可能会抛出FileNotFoundException的异常。我们的编译器会检查，发现我们既没有声明异常，也没有抛出，这样就会报错。

public class Test {
	public static void main(String[] args) {
		File f = new File("file.txt");
		try {
			FileInputStream input = new FileInputStream(f);
		} catch (FileNotFoundException e) {
			e.printStackTrace();
		}
		
	}

}