Biegral Blog

异常处理

1、IO文件不存在

import java.io.FileNotFoundException;
import java.io.FileReader;

public class TestError {
	public static void main(String[] args) throws FileNotFoundException {
		FileReader fr = new FileReader("D:\\aa.text");
	}
}

2、就地解决异常

import java.io.FileNotFoundException;
import java.io.FileReader;

public class TestError {
	public static void main(String[] args) {
		try {
			FileReader fr = new FileReader("D:\\aa.text");
		} catch (FileNotFoundException e) {
			// TODO Auto-generated catch block
			e.printStackTrace();
		}
	}
}

public class TestError {
	public static void main(String[] args) {
		try {
			FileReader fr = new FileReader("D:\\aa.text");
			Socket s = new  Socket("192.168.1.1", 78);
		} catch (FileNotFoundException e) {
			// TODO Auto-generated catch block
			e.printStackTrace();
		} catch (IOException e) {
			// TODO Auto-generated catch block
			e.printStackTrace();
		} 
	}
}

public class TestError {
	public static void main(String[] args) {
		try {
			FileReader fr = new FileReader("D:\\aa.text");
			Socket s = new  Socket("192.168.1.1", 78);
		} catch (Exception e) {
			// TODO Auto-generated catch block
			e.printStackTrace();
		}
	}
}

如果抛出异常，那么就终止执行代码，

如何进入actch，如果有多个catch语句，则进入匹配那个。

一般把需要关闭的资源。[文件，连接。内存……]放在finally里面

import java.io.FileReader;
import java.net.Socket;

public class TestError {
	public static void main(String[] args) {
		FileReader fr = null;
		try {
			fr = new FileReader("D:\\aa.txt");
			Socket s = new  Socket("192.168.1.1", 78);
		} catch (Exception e) {
			// TODO Auto-generated catch block
			e.printStackTrace();
		} finally {
			System.out.println("finally");
			if (fr != null) {
				try {
					fr.close();
				} catch (Exception e2) {
					e2.printStackTrace();
					// TODO: handle exception
				}
			}
		}
	}
}

注意：finally不一定要放在catch后面，也可以直接放在try后面不要catch，但是不常见。

3、抛出异常

import java.io.FileNotFoundException;
import java.io.FileReader;

public class TestError {
	public static void main(String[] args) <span style="color:#ff0000;"><strong>throws FileNotFoundException</strong></span> {
		FileReader fr = new FileReader("D:\\aa.text");
	}
}