一文带你快速读懂Java中的异常

FileOutputStream out = null; 
try { 
  out = new FileOutputStream("abc.text"); 
  out.write(1); 
  System.out.println("写入成功"); 
} catch (FileNotFoundException e) { 
   
  System.out.println("要写入的文件不存在"); 
  e.printStackTrace(); 
   
} catch (IOException e) { 
   
  System.out.println("发生了IO错误"); 
  e.printStackTrace(); 
   
}finally{ 
  if(out != null){ 
    try { 
      out.close(); 
    } catch (IOException e) { 
      e.printStackTrace(); 
    } 
  } 
} 

public class Travel { 
  private static int power = 100; 
  private static boolean bridgeIsOk = true; 
  public static void main(String[] args) { 
    //描述一下坐火车旅游的过程 
    System.out.println("从济南出发， 到北京旅游"); 
    System.out.println("列车开到德州"); 
    //中途给妈妈打个电话 
    try{ 
      telToMom(); 
    }catch(BatteryDiedException e){ 
      System.out.println("换一块电池， 继续旅程"); 
    } 
    //桥断了 
    if(!bridgeIsOk){ 
      System.out.println("旅程结束"); 
      throw new BridgeBreakError("桥断了，列车停止运行"); 
    } 
    System.out.println("到北京站，下车"); 
    //下雨了 
    try{ 
      throw new RainException("下雨了"); 
    }catch(RainException e){ 
      System.out.println("撑起准备的雨伞， 继续旅程"); 
    } 
  } 
  private static void telToMom() throws BatteryDiedException{ 
    if(power == 0){ //手机电量为0 
      System.out.println("手机没电了"); 
      throw new BatteryDiedException("手机没电了"); 
    } 
    System.out.println("给妈妈打电话"); 
  } 
  static class BatteryDiedException extends Exception{ 
    public BatteryDiedException(String msg){ 
      super(msg); 
    } 
  } 
  static class BridgeBreakError extends Error{ 
    public BridgeBreakError(String msg){ 
      super(msg); 
    } 
  } 
  static class RainException extends Exception{ 
    public RainException(String msg){ 
      super(msg); 
    } 
  } 
} 

public static Class<&#63;> forName(String className)  
      throws ClassNotFoundException { 
  return forName0(className, true, ClassLoader.getCallerClassLoader()); 
} 

try { 
  Class clazz = Class.forName("com.bjpowernode.Person"); 
} catch (ClassNotFoundException e) { 
   
  System.out.println("Person类加载失败"); 
  System.exit(0); 
  e.printStackTrace(); 
}

private static boolean isSick = true; 
public static void main(String[] args) { 
  if(isSick){ 
    System.out.println("生病了，旅途中止"); 
    throw new SickException("病了"); 
  } 
} 
private static class SickException extends RuntimeException{ 
  public SickException(String msg){ 
    super(msg); 
  } 
} 

public static void main(String[] args) { 
  caculateSalary(3); 
} 
 
/** 
 * 计算一个月的薪资 
 * @param month 月份 
 */ 
public static void caculateSalary(int month){ 
   
  //如果参数错误， 抛出非法参数异常 
  if(month < 1 || month > 12){ 
    throw new IllegalArgumentException(); 
  } 
} 
 
private static void caculateSalaryInner(int month){ 
  //计算薪资 ... 
} 

public static void main(String[] args) { 
  doSomething(); 
} 
public static void doSomething(){ 
  Object obj = null; 
  try { //运行时异常也是可以捕获的 
    obj.toString(); 
  } catch (RuntimeException e) { 
    System.out.println("抛出了运行时异常, 异常的具体类型：" + e.getClass().getName()); 
  } 
} 

public static void main(String[] args) { 
  doSomething();  //不必处理方法声明抛出的运行时异常 
} 
 
public static void doSomething() throws RuntimeException{ 
   
  throw new RuntimeException(); 
} 

public class DoWork { 
  public static class Boss{  //老板 
    private Employee emp; //员工对象 
    public Boss(Employee emp){ 
      this.emp = emp; 
    } 
    public void doWork(){  
      try { 
        emp.doWork();  //老板委托员工外出执行任务,给员工块钱的经费 
      } catch (TaskCannotCompleteException e) {  //任务无法完成 
        System.out.println("派出另一个员工去完成任务"); 
      }  
    } 
  } 
  public static class Employee{  //员工 
    //执行任务，可能不能完成任务 
    public void doWork(float money) throws TaskCannotCompleteException{ 
      //  
      if(money < ){  //经费太少，无法执行任务 
        throw new MoneyNotEnoughException(); 
      } 
      // 
      try { 
        goToWorkPlace(); 
      } catch (CannotFindBusException e) { //在去工作地点时找不到公交车 
        System.out.println("打车去"); 
      } 
      // 
      try { 
        workDayAndNight(); 
      } catch (TiredToSickException e) { //累病了 
        //告诉老板，任务无法完成 
        throw new TaskCannotCompleteException(); 
      } 
    } 
    //在去工作地点时可能找不到公交车 
    private void goToWorkPlace() throws CannotFindBusException{ 
      //throw new CannotFindBusException(); 
    } 
    //没天没夜的干活， 可能会累病 
    private void workDayAndNight() throws TiredToSickException{ 
      //throw new TiredToSickException(); 
    } 
  } 
  //找不到公交车异常 
  public static class CannotFindBusException extends Exception{} 
  //经费不足异常 
  public static class MoneyNotEnoughException extends RuntimeException{} 
  //累病异常 
  public static class TiredToSickException extends Exception{} 
  //任务无法完成异常 
  public static class TaskCannotCompleteException extends Exception{} 
  public static void main(String[] args) { 
    Boss boss = new Boss(new Employee()); 
    boss.doWork(); 
  } 
}