How can I throw a general exception in Java?

Question

Consider this simple program. The program has two files:

File Vehicle.java

class Vehicle {     private int speed = 0;     private int maxSpeed = 100;      public int getSpeed()     {         return speed;     }      public int getMaxSpeed()     {         return maxSpeed;     }      public void speedUp(int increment)     {         if(speed + increment > maxSpeed){             // Throw exception         }else{             speed += increment;         }     }      public void speedDown(int decrement)     {         if(speed - decrement < 0){             // Throw exception         }else{             speed -= decrement;         }     } } 

File HelloWorld.java

public class HelloWorld {      /**      * @param args      */     public static void main(String[] args) {          Vehicle v1 = new Vehicle();         Vehicle v2 = new Vehicle();              // Do something              // Print something useful, TODO         System.out.println(v1.getSpeed());     }  } 

As you can see in the first class, I have added a comment ("// throw exception") where I would like to throw an exception. Do I have to define my own class for exceptions or is there some general exception class in Java I can use?

Answer 1

You could create your own Exception class:

public class InvalidSpeedException extends Exception {    public InvalidSpeedException(String message){      super(message);   }  } 

In your code:

throw new InvalidSpeedException("TOO HIGH"); 

Answer 2

You could use IllegalArgumentException:

public void speedDown(int decrement) {     if(speed - decrement < 0){         throw new IllegalArgumentException("Final speed can not be less than zero");     }else{         speed -= decrement;     } }