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BuilderWithConditionalException

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(→Throw on I/O Error)
(→Throw on I/O Error)
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=== Throw on I/O Error ===
=== Throw on I/O Error ===
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The builder pattern delays reading of the actual file up until the ''build()'' method is called. As reading of a file means an I/O operation and as each I/O operation in Java may yield [[checked exception|checked]] {{JDK|java/io|IOException}}, it is desirable for the ''build()'' method to propagate it to the caller.
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The builder pattern delays reading of the actual file up until the ''build()'' method is called. As reading of a file means an I/O operation and as each I/O operation in Java may yield [[checked exception|checked]] {{JDK|java/io|IOException}}, it is desirable for the ''build()'' method to propagate it to the caller:
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<source lang="java">
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public Source build() throws IOException {
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// construct and
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return source;
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}
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</source>
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However there is more. The [[builder]] may also construct a {{truffle|com/oracle/truffle/api/source|Source} object from already provided text. The usage looks like:

Revision as of 13:28, 10 June 2016

The builder pattern is gaining more and more popularity in the APIs that I design: In Truffle API we are trying to use it a lot. For example an instance of the PolyglotEngine is constructed via a builder obtained from its newBuilder() method.

Builder for Source

These days I am trying to use the builder pattern also for construction of Source. Rather than having various (and overloaded) methods with fromFileName, etc. we'd like to have: 

Source source = Source.newFromFile(file).
   mimetype("text/javascript").
   name("FancyName.js").
   build();

It works fine and allows the users to specify only those properties that are needed - for example one can omit the name - then it would be derived from the name of the file. The same applies to mimetype.

Throw on I/O Error

The builder pattern delays reading of the actual file up until the build() method is called. As reading of a file means an I/O operation and as each I/O operation in Java may yield checked IOException, it is desirable for the build() method to propagate it to the caller: 

public Source build() throws IOException {
   // construct and
   return source;
}

However there is more. The builder may also construct a {{truffle|com/oracle/truffle/api/source|Source} object from already provided text. The usage looks like:

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