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Exceptions

lib/exceptions/ defines the exception hierarchy.

Hierarchy​

Exception
├── RuntimeException
│   ├── IllegalArgumentException
│   ├── IndexOutOfBoundsException
│   ├── NullPointerException
│   └── ClassNotFoundException
└── (your custom exception classes)

All exceptions extend Exception and carry a message accessible via getMessage().

Throwing​

import * from "lib/exceptions/IllegalArgumentException.mt";

if (input == "") {
    throw new IllegalArgumentException("input cannot be empty");
}

Catching​

import * from "lib/exceptions/Exception.mt";

try {
    risky();
} catch (Exception e) {
    print("error: " + e.getMessage());
}

A single try can have multiple catch clauses for different exception types; the first compatible one runs.

Custom Exceptions​

import * from "lib/exceptions/Exception.mt";

class ValidationException extends Exception {
    public constructor(string message): super(message) { }
}

Declare what a method throws using @Throw:

@Throw(exceptions = [ValidationException])
public function validate(string input): bool { ... }

Network Exceptions​

lib/net/exceptions/ provides network-specific subclasses:

  • NetworkException
  • ConnectionException
  • DnsException
  • HttpException
  • TimeoutException

See Network for how they're raised.

See Also​