异常机制详解

常见异常分类：

一，Throwable（可投掷的，抛出。）:

1，Error（错误）:硬件出现问题

2，Exception(异常):

编译异常：

Class（类）Not（不是）Found（成立）Exception：找不到类异常IO（IO）Exception（异常）：IO异常File（文件）Not（不是）Found（成立）Exception：找不到文件异常

Runtime(运行)Exception(异常)：

Class（类）Cast（投掷）Exception（异常）：类转换异常Null（空）Pointer（指针）Exception（异常）：空指针异常Array（数组）Index（索引）Out（出去）Of（的）BoudsException（异常）：数组索引越界异常File（文件)System（系统）Not（不是）Found（成立）Exception（异常）：找不到文件系统异常Arithmetic（算数）Exception（异常）：算数异常Number（数字）Format（格式）Exception（异常）：数字格式异常

异常处理：

异常处理流程：

程序中产生异常后，Jvm根据异常的类型实例化异常类的对象；若程序中不存在异常处理操作，则这个实例化的对象的默认处理方式是jvm进行异常的信息的输出，而后终端程序。存在异常处理，由try语句捕获该异常对象，与程序后面的catch进行匹配，匹配失败则交由JVM进行处理。有无异常都会执行finally中的程序，若无异常，finally语句执行完后继续后面的程序语句；若存在没有能够处理的异常对象，finally语句会交给JVM进行信息的输出，并且中断程序。

编译时异常处理方式：

1，throws（投掷）关键字处理：

当前方法不用处理该异常对象，可以直接将异常对象抛出给他的调用者（上级），由上级处理，若所有调用者都没处理或（最顶级的调用者main方法里都没有处理该异常），则由JVM输出异常信息程序中断。

2，try{...}catch{...}finally{...}

语句处理格式：

try{

可能出现异常的代码块，范围越少越好

}catch（异常类型  异常对象名）{

异常处理语句；

}finally{

需要释放的资源；

}

Static public void main(String[] args){
    try{
    System.out.println("aaa");
        Trycat.cot();
    }catch(ArithmeticException e){
        e.printStackTrace();
    }finally{
    System.out.println("此行代码一定会被执行");
    }

}
private static void cot() throws ArithmeticException{
    int i = 10,j = 0;
    int k = i/j;
}

运行结果：

"C:Program FilesJavajdk1.8.0_311binjava.exe" "-javaagent:C:Users蜡笔小新IntelliJ IDEA Community Edition 2021.3.2libidea_rt.jar=56723:C:Users蜡笔小新IntelliJ IDEA Community Edition 2021.3.2bin" -Dfile.encoding=UTF-8 -classpath "C:Program FilesJavajdk1.8.0_311jrelibcharsets.jar;C:Program FilesJavajdk1.8.0_311jrelibdeploy.jar;C:Program FilesJavajdk1.8.0_311jrelibextaccess-bridge-64.jar;C:Program FilesJavajdk1.8.0_311jrelibextcldrdata.jar;C:Program FilesJavajdk1.8.0_311jrelibextdnsns.jar;C:Program FilesJavajdk1.8.0_311jrelibextjaccess.jar;C:Program FilesJavajdk1.8.0_311jrelibextjfxrt.jar;C:Program FilesJavajdk1.8.0_311jrelibextlocaledata.jar;C:Program FilesJavajdk1.8.0_311jrelibextnashorn.jar;C:Program FilesJavajdk1.8.0_311jrelibextsunec.jar;C:Program FilesJavajdk1.8.0_311jrelibextsunjce_provider.jar;C:Program FilesJavajdk1.8.0_311jrelibextsunmscapi.jar;C:Program FilesJavajdk1.8.0_311jrelibextsunpkcs11.jar;C:Program FilesJavajdk1.8.0_311jrelibextzipfs.jar;C:Program FilesJavajdk1.8.0_311jrelibjavaws.jar;C:Program FilesJavajdk1.8.0_311jrelibjce.jar;C:Program FilesJavajdk1.8.0_311jrelibjfr.jar;C:Program FilesJavajdk1.8.0_311jrelibjfxswt.jar;C:Program FilesJavajdk1.8.0_311jrelibjsse.jar;C:Program FilesJavajdk1.8.0_311jrelibmanagement-agent.jar;C:Program FilesJavajdk1.8.0_311jrelibplugin.jar;C:Program FilesJavajdk1.8.0_311jrelibresources.jar;C:Program FilesJavajdk1.8.0_311jrelibrt.jar;D:yuanchangqiproject01outproduction异常" com.yichang.TryCat
aaaa
此行代码一定会被执行
java.lang.ArithmeticException: / by zero
	at com.yichang.TryCat.cout(TryCat.java:16)
	at com.yichang.TryCat.main(TryCat.java:7)

进程已结束,退出代码0

3.throw 关键字自定义异常

（1）手动抛出异常

public class Throws {
    public static void main(String[] args) {
        Student sut = new Student();
        try{
            sut.regIst(-30);
        }catch(Exception e){
            //e.printStackTrace();
            System.out.println(e.getMessage());//通过Exception的构造器方法输出
        }
        System.out.println(sut);
    }
}
class Student{
    private int id;
    public void regIst(int id) throws Exception {
        //throw new runtimeException("您输入了非法数字");
        // 运行时异常可以直接抛出，在运行时解决异常就可以了，运行时异常可以不处理，报错就行了
        if (id > 0){
            this.id = id;
        }else throw new Exception("您输入了非法数字");//编译时异常必须处理

运行结果

"C:Program FilesJavajdk1.8.0_311binjava.exe" "-javaagent:C:Users蜡笔小新IntelliJ IDEA Community Edition 2021.3.2libidea_rt.jar=57855:C:Users蜡笔小新IntelliJ IDEA Community Edition 2021.3.2bin" -Dfile.encoding=UTF-8 -classpath "C:Program FilesJavajdk1.8.0_311jrelibcharsets.jar;C:Program FilesJavajdk1.8.0_311jrelibdeploy.jar;C:Program FilesJavajdk1.8.0_311jrelibextaccess-bridge-64.jar;C:Program FilesJavajdk1.8.0_311jrelibextcldrdata.jar;C:Program FilesJavajdk1.8.0_311jrelibextdnsns.jar;C:Program FilesJavajdk1.8.0_311jrelibextjaccess.jar;C:Program FilesJavajdk1.8.0_311jrelibextjfxrt.jar;C:Program FilesJavajdk1.8.0_311jrelibextlocaledata.jar;C:Program FilesJavajdk1.8.0_311jrelibextnashorn.jar;C:Program FilesJavajdk1.8.0_311jrelibextsunec.jar;C:Program FilesJavajdk1.8.0_311jrelibextsunjce_provider.jar;C:Program FilesJavajdk1.8.0_311jrelibextsunmscapi.jar;C:Program FilesJavajdk1.8.0_311jrelibextsunpkcs11.jar;C:Program FilesJavajdk1.8.0_311jrelibextzipfs.jar;C:Program FilesJavajdk1.8.0_311jrelibjavaws.jar;C:Program FilesJavajdk1.8.0_311jrelibjce.jar;C:Program FilesJavajdk1.8.0_311jrelibjfr.jar;C:Program FilesJavajdk1.8.0_311jrelibjfxswt.jar;C:Program FilesJavajdk1.8.0_311jrelibjsse.jar;C:Program FilesJavajdk1.8.0_311jrelibmanagement-agent.jar;C:Program FilesJavajdk1.8.0_311jrelibplugin.jar;C:Program FilesJavajdk1.8.0_311jrelibresources.jar;C:Program FilesJavajdk1.8.0_311jrelibrt.jar;D:yuanchangqiproject01outproduction异常" com.yichang.Throws
您输入了非法数字
com.yichang.Student@1b6d3586

进程已结束,退出代码0

throw小结：throw只能抛出一个异常类的对象

（2）自定义异常：

public class MyException extends RuntimeException {
    static final long serialVersionUID = -703786464564L;

    public MyException() {
    }

    public MyException(String msg) {
        super(msg);
    }
}
public class Throws02 {
    public static void main(String[] args) {
        Student stu = new Student();
        try {
            stu.regIst(-30);
        } catch (Exception e) {
            e.printStackTrace();
        }
    }
}
class Student02{
    private int id;
    public void regIst(int id)throws MyException{
        if(id > 0){
            this.id = id;
        }else throw new MyException("您输入了非法数字");
    }
}

运行结果：

"C:Program FilesJavajdk1.8.0_311binjava.exe" "-javaagent:C:Users蜡笔小新IntelliJ IDEA Community Edition 2021.3.2libidea_rt.jar=58133:C:Users蜡笔小新IntelliJ IDEA Community Edition 2021.3.2bin" -Dfile.encoding=UTF-8 -classpath "C:Program FilesJavajdk1.8.0_311jrelibcharsets.jar;C:Program FilesJavajdk1.8.0_311jrelibdeploy.jar;C:Program FilesJavajdk1.8.0_311jrelibextaccess-bridge-64.jar;C:Program FilesJavajdk1.8.0_311jrelibextcldrdata.jar;C:Program FilesJavajdk1.8.0_311jrelibextdnsns.jar;C:Program FilesJavajdk1.8.0_311jrelibextjaccess.jar;C:Program FilesJavajdk1.8.0_311jrelibextjfxrt.jar;C:Program FilesJavajdk1.8.0_311jrelibextlocaledata.jar;C:Program FilesJavajdk1.8.0_311jrelibextnashorn.jar;C:Program FilesJavajdk1.8.0_311jrelibextsunec.jar;C:Program FilesJavajdk1.8.0_311jrelibextsunjce_provider.jar;C:Program FilesJavajdk1.8.0_311jrelibextsunmscapi.jar;C:Program FilesJavajdk1.8.0_311jrelibextsunpkcs11.jar;C:Program FilesJavajdk1.8.0_311jrelibextzipfs.jar;C:Program FilesJavajdk1.8.0_311jrelibjavaws.jar;C:Program FilesJavajdk1.8.0_311jrelibjce.jar;C:Program FilesJavajdk1.8.0_311jrelibjfr.jar;C:Program FilesJavajdk1.8.0_311jrelibjfxswt.jar;C:Program FilesJavajdk1.8.0_311jrelibjsse.jar;C:Program FilesJavajdk1.8.0_311jrelibmanagement-agent.jar;C:Program FilesJavajdk1.8.0_311jrelibplugin.jar;C:Program FilesJavajdk1.8.0_311jrelibresources.jar;C:Program FilesJavajdk1.8.0_311jrelibrt.jar;D:yuanchangqiproject01outproduction异常" com.yichang.Throws02
您输入了非法数字

进程已结束,退出代码0