class Person {
    public Person() {
        
    }
    int age;
    public void setAge(int age) throws AgeOutOfBoundException  {　　　　//正常code
        if (age>=0) {
            this.age = age;    
        }
        else {
            throw new AgeOutOfBoundException(age);
        }
    }
    
}
class AgeOutOfBoundException extends Exception {
    public AgeOutOfBoundException(int age) {
        // TODO Auto-generated constructor stub
        super(String.valueOf(age));
    }
}

編譯報錯code

class Person {
    public Person() {
        
    }
    int age;
    public void setAge(int age) {　　　　//異常code
        if (age>=0) {
            this.age = age;    
        }
        else {
            throw new AgeOutOfBoundException(age);
        }
    }
    
}
class AgeOutOfBoundException extends Exception {
    public AgeOutOfBoundException(int age) {
        // TODO Auto-generated constructor stub
        super(String.valueOf(age));
    }
}

原因：

在某個方法中，假如使用了throwable類，必須得對部分程式碼做try catch或者宣告這一段會發生異常。
所以必須新增throw ...Exception.