复习java基础第二天(异常处理)

public class TestException {
    
    public static void main(String[] args) {
        
        int i = 10;
        //数学异常: java.lang.ArithmeticException
        int j = i / 0;
        System.out.println(j); 
    
        int [] scores = new int[]{1, 2, 4, 5};
        //数组下标越界异常: java.lang.ArrayIndexOutOfBoundsException
        System.out.println(scores[4]); 
        
        Person p1 = new Man();
        //类型转换异常: java.lang.ClassCastException
        Woman p2 = (Woman) p1;
        
        p1 = null;
        //空指针异常: java.lang.NullPointerException
        System.out.println(p1.toString()); 
        
        System.out.println("end...");
    }    
}

class Person{
    
}

class Man extends Person{
    
}

class Woman extends Person{
    
}

import java.io.FileNotFoundException;
import java.io.InputStream;

public class TestTryCatchFinally {
    
    public static void main(String[] args) {
        
        try {
            int i = 10;
            int j = i / 0;
        } finally{
             System.out.println("finally...");
         }
        
        //不论在try、catch代码块中是否发生了异常事件，finally块中的语句都会被执行。        
        System.out.println("end...");
        
        //示例编译时异常, IO 异常属于编译时异常.       
        try {
            InputStream is = new FileInputStream("abc.txt");
        } catch (FileNotFoundException e) {
            e.printStackTrace();
        }
    }  
}

import java.io.FileNotFoundException;
import java.io.IOException;

public class TestThrows {

    public static void main(String[] args) {
        try {
            test();
        } catch (Exception e) {
            e.printStackTrace();
        }
    }
 
    public static void test(){ 
        
        int i = 10 / 0;
        System.out.println(i);
         
//        InputStream fs = new FileInputStream("abc.txt"); 
        
//        Connection connection = null;
//        String sql = null;
//        PreparedStatement ps = connection.prepareStatement(sql);
        
//        byte [] buffer = new byte[fs.available()];
//        fs.read(buffer);
        
        A a = new B();
        try {
            a.method();
        } catch (FileNotFoundException e) {
            e.printStackTrace();
        }       
    }    
}

class A{
    void method () throws FileNotFoundException{        
    }
}

class B extends A{
//    @Override
//    void method() throws IOException {
//    }
}

import java.util.Scanner;

public class TestThrow {

    public static void main(String[] args) {
        try {
            inputAge();
        } catch (Exception e) {
            System.out.println(e.getMessage()); 
        }      
        System.out.println("end...");
    }
    
    /**
     * 输入年纪: 要求年纪必须在 15-30 之间, 超出 30 则年纪偏大
     */
    public static void inputAge(){
        Scanner sc = new Scanner(System.in);       
        System.out.print("age=");
        int age = sc.nextInt();
        
        if(age > 30){
//          System.out.println("年纪偏大.");
            throw new AgeTooLargeException("年纪偏大.");
        }
    }

    public static void test(){
        
        //1. 创建一个异常类对象
        RuntimeException ex = new RuntimeException();
        
        //2. 把异常类对象抛出去
        throw ex;
    }   
}

public class EcDef extends RuntimeException{

    public EcDef() {
        // TODO Auto-generated constructor stub
    }
    
    public EcDef(String msg) {
        super(msg);
    }

}

public class EcmDef {

    public static void main(String[] args) {
        
        try {
            int i = Integer.parseInt(args[0]); // "a"
            int j = Integer.parseInt(args[1]);
            
            System.out.println(ecm(i, j));
        } catch (ArrayIndexOutOfBoundsException e) {
            System.out.println("输入的参数个数不足.");
        } catch (ArithmeticException e) {
            System.out.println("除数不能为 0");
        } catch (EcDef e) {
            System.out.println(e.getMessage()); 
        } catch (NumberFormatException e) {
            System.out.println("输入的参数不能转为整型.");
        }
    }
    
    public static int ecm(int i, int j){
        
        if(i < 0 || j < 0){
            throw new EcDef("不能处理负数. ");
        }
        
        int result = i / j;
        return result;
    }
}