java中异常的分类

àì夳堔傛蜴生んèń 2022-04-06 09:17 285阅读 0赞

# java中异常的分类 #

一个图，五个关键字

try、catch、finally、throw、throws  
![df335993-734b-351f-9361-06f8763b4dd7.png][]

TestExceptions.java

//异常
    public class TestExceptions {
    	public static void main(String[] args) {
    		TestExceptions te = new TestExceptions();
    		te.m(0);
    	}
    	//throws抛出ArithmeticException
    	void m(int i) throws ArithmeticException {
    		if(i==0) { 
    			//定义ArithmeticException的消息
    			throw new ArithmeticException("被除数为0");
    		}
    	}
    }

F:\java>javac TestExceptions.java
    
    F:\java>java TestExceptions
    Exception in thread "main" java.lang.ArithmeticException: 被除数为0
            at TestExceptions.m(TestExceptions.java:11)
            at TestExceptions.main(TestExceptions.java:5)
    
    F:\java>

使用try...catch捕捉异常

TestExceptions.java

//异常
    public class TestExceptions {
    	public static void main(String[] args) {
    		try {
    			new TestExceptions().m(0);
    		} catch (ArithmeticException ae) {
    			ae.printStackTrace();
    			System.out.println("出错了");
    		}
    	}
    	//throws抛出ArithmeticException
    	void m(int i) throws ArithmeticException {
    		if(i==0) { 
    			//定义ArithmeticException的消息
    			throw new ArithmeticException("被除数为0");
    		}
    	}
    }

F:\java>javac TestExceptions.java
    
    F:\java>java TestExceptions
    java.lang.ArithmeticException: 被除数为0
            at TestExceptions.m(TestExceptions.java:15)
            at TestExceptions.main(TestExceptions.java:5)
    出错了
    
    F:\java>

必须要捕捉的异常

TestExceptions.java

import java.io.*;
    
    //异常
    public class TestExceptions {
    	public static void main(String[] args) {
    		//io包下的一个类
    		FileInputStream in = null;
    		//一个try可以跟多个catch
    		try {
    			//必须要捕捉FileNotFoundException异常
    			in = new FileInputStream("myfile.txt");
    			int b;
    			b = in.read();
    			while (b != -1) {
    				System.out.print((char) b);
    				b = in.read();
    			}
    		} catch (FileNotFoundException e) {
    			System.out.println(e.getMessage());
    
    		} catch (IOException e) {
    			e.printStackTrace(); 
    		} finally {
    			try {
    				in.close();
    			} catch (IOException e) {
    				e.printStackTrace();
    			}
    		}
    	}
    }

myfile.txt存在时

F:\java>javac TestExceptions.java
    
    F:\java>java TestExceptions
    a
    ab
    abc
    abcd
    F:\java>

myfile.txt不存在时

F:\java>javac TestExceptions.java
    
    F:\java>java TestExceptions
    myfile.txt (系统找不到指定的文件。)
    Exception in thread "main" java.lang.NullPointerException
            at TestExceptions.main(TestExceptions.java:25)
    
    F:\java>

myfile.txt

a
    ab
    abc
    abcd

[df335993-734b-351f-9361-06f8763b4dd7.png]: /images/20220406/1dd2c12fd0bf47ddbe537609eb1adef5.png