java新手笔记23 异常

1.import

package com.yfs.javase;



import java.util.Scanner;



//import java.lang.String;//默认导入

public class Demo1 {

	

	public static void main(String[] args) {

		String s = new String("abc");//java.lang.String

		String s1 = "abc";



		System.out.println("影分身");//输出

		Scanner scan = new Scanner(System.in);//输入

		System.err.println("我没错...");//错误流

		

		long now = System.currentTimeMillis();

		System.out.println("系统时间  " + String.format("%tF %<tT",  now));

	    //System.exit(0);

		

		System.out.println (System.getenv("java_home"));

	    

	    System.out.println("程序执行到此...");

	

	}



}

 2.异常

package com.yfs.javase;

//异常

//执行出现异常 jvm 终止代码执行 

//报告错误原因 

//机制 

public class ExpDemo1 {

	

	public static void main(String[] args) {

		String s = null;//没有对象

		//s.toString();//NullpointException

		int[] a = new int[5];

		//a[5] = 20; //ArrayIndexOutOfBoundsException

		

		int b = 3;

		int c = 0;

		int d = b / c;//ArithmeticException

		

		

		System.out.println("程序执行结束...");

	}

	

	

}

 3.运行时异常

Person 类

package com.yfs.javase;



public class Person {



	private String name;

	private int age;

	private char sex;



	public Person() {

		

	}



	public Person(String name) {

		this.name = name;

	}



	public Person(String name, int age, char sex) {

		this.name = name;

		this.age = age;

		this.sex = sex;

	}



	public void introduce() {

		System.out.println("I am Person....");

	}



	public String toString() {

		return "姓名：" + name + "  年龄 ：" + age + "  性别：" + sex;

	}



	public void speak() {

		System.out.println(name + " 工件了吗？");

	}



	public void sleep() {

		System.out.println(name + " 睡觉了吗？");

	}



	public void eat() {

		System.out.println(name + " 吃了吗？");

	}



	public String getName() {

		return name;

	}



	public void setName(String name) {

		this.name = name;

	}



	public int getAge() {

		return age;

	}



	public void setAge(int age) {

		this.age = age;

	}



	public char getSex() {

		return sex;

	}



	public void setSex(char sex) {

		this.sex = sex;

	}



}

 类转换异常

package com.yfs.javase;



import java.io.FileInputStream;

import java.io.FileNotFoundException;

import java.io.InputStream;



//异常分类



public class ExpDemo2 {



	public static void main(String[] args) {

		// 运行时异常

		Object obj = new Person();

		// String s = (String)obj;//ClassCastException

		

		// check异常 编译时强制处理

		try {

			InputStream in = new FileInputStream("123.txt");

		} catch (FileNotFoundException e) {

			System.out.println("异常处理完成...");

			e.printStackTrace();

		}



		System.out.println("程序执行结束...");

	}



}

 4.抛异常

package com.yfs.javase;



import java.io.FileInputStream;

import java.io.FileNotFoundException;

import java.io.InputStream;

import java.sql.SQLException;



//抛异常



public class ExpDemo3 {



	public static void main(String[] args) throws FileNotFoundException {

		// 谁调用谁处理 没有对象处理 jvm处理 终止程序

		// try {

		try {

			test();

		} catch (SQLException e) {

			// TODO Auto-generated catch block

			e.printStackTrace();

		}

		// } catch (FileNotFoundException e) {

		// e.printStackTrace();

		// }

	}



	// 在方法抛出异常  throws 可以抛多个异常

	public static void test() throws FileNotFoundException, SQLException {

		int[] a = new int[3];

		a[3] = 15;// 系统检查抛出异常



		// 自己抛 throw

		if (1 == 1) {

			throw new ArithmeticException("故意抛异常");

		}

		// check 异常

		InputStream in = new FileInputStream("123.txt");

	}

}

 5.异常处理

package com.yfs.javase;



import java.io.FileInputStream;

import java.io.FileNotFoundException;

import java.io.InputStream;

import java.sql.SQLException;



//异常处理  catch  捕获异常对象  处理异常



public class ExpDemo4 {



	public static void main(String[] args) {

		String s = "abc";

		int[] a = new int[3];

		//try...catch...finally

	    try{

			a[3] = 15;//jvm创建异常对象  抛出异常  处理第一个异常

			s.toString();

			//可以有多个catch语句块

	    }  

//	    catch (ArrayIndexOutOfBoundsException e) {//捕获异常

//			//e.printStackTrace();

//	    	System.out.println("我知道了..我是故意的");

//		} catch (NullPointerException e) {

//			System.out.println("字符串异常处理完成...");

//		} catch (Exception e) {

//			e.printStackTrace();

//			// finally 总会执行

//		} 

	    finally {

			System.out.println("总是执行....");

		}

		



		

		System.out.println("程序执行结束...");

	}



	

}

 6.自定义异常

package com.yfs.javase;

//自定义异常

public class ExpSelf extends Exception {



	public ExpSelf() {

		super();

		// TODO Auto-generated constructor stub

	}



	public ExpSelf(String message, Throwable cause, boolean enableSuppression,

			boolean writableStackTrace) {

		super(message, cause, enableSuppression, writableStackTrace);

		// TODO Auto-generated constructor stub

	}



	public ExpSelf(String message, Throwable cause) {

		super(message, cause);

		// TODO Auto-generated constructor stub

	}



	public ExpSelf(String message) {

		super(message);

		// TODO Auto-generated constructor stub

	}



	public ExpSelf(Throwable cause) {

		super(cause);

		// TODO Auto-generated constructor stub

	}

	//String参数的构造方法

//	public ExpSelf(String msg) {

//		super(msg);//调用父类构造方法

//	}

	



}

 7.自定义异常 测试

package com.yfs.javase;



import java.io.IOException;



public class Test {



	public static void main(String[] args) {

		try {

			if( 1 == 1) {

				throw  new ExpSelf("异常了，自己定义的...", new IOException());

			}

		} catch (ExpSelf e) {

			//e.printStackTrace();

			System.out.println(e.getMessage());

			System.out.println(e.fillInStackTrace());

			System.out.println(e.toString());

		}



	}



}