Method chaining

Author: Kasper B. Graversen, 21/06/08 Keywords: Method chaining, Shortcut programming Abstract: Method chaining enables terser and more natural interaction with objects. Despite it has been around in languages such as Smalltalk since the 1960's it has been "forgotten" in main stream languages such as Java, C# and Python.

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Method chaining

class MyBean {
	String getAddress() { ... }
	void setName(String name) { ... }
	void setAddress(String adr) { ... }
	...
}

MyBean bean = new MyBean();
bean.setName("foo");
bean.setAddress("bar");

HashMap map = new HashMap();
h.put("bar", 1);
foo(h);

Calendar c = Calendar.getInstance();
c.set(2007, 2, 28);
c.setMillis(0);
foo(c);

foo( new HashMap().put("bar", 1) );

foo( Calendar.getInstance().set(2007, 2, 28).setMillis(0) );

Applying Method Chaining

MyBean bean = new MyBean()
.setName("foo")
.setAddress("bar);

MyBean bean = new MyBean().setName("foo").setAddress("bar);

foo( new Hashtable().put("bar", 1) );

Where to apply?

Drawbacks

• There is a bit more to cod, since set-methods now has to contain a return statement, and IDE's such as Eclipse still only supports generating simple set-methods returning void. So potentially, you need to revise code that would otherwise be automatically generated.
• Many debuggers operate on a line basis rather than on pr. expression, hence when you have a really long chain, it may be hard to step through...
• If you have a core of a framework, reading the API in Javadoc may be a bit hard at times. The problem is that you have tailored your framework to be used in combination with other enities, not to be read in isolation. This, however, is more a problem with fluint interfaces rather than method chaining.
• The pattern doesn't lend itself well to older versions of Java (pre Java 5), due to the lack of support for covariant return types of methods. That is, an overridding method in a subclass may wish to return something of a more specialized type (itself, which is more specialized as it is aa sub type :-). In such cases, your code requires using casts which is far from nice, hence review those situations and don't apply the pattern if things become too ugly for your taste.

Going full circle

The Spiffy Framework

class C {
    ArrayList<String> excludedFiles = CollectionHelper.arrayList("index.xml", "index-all.xml", "menu.xml");
}

class C {
    public List<String> excludeDirNames = new ArrayList<String>();
    public C() {
      excludedFiles.add("index.xml");
      excludedFiles.add("index-all.xml");
      excludedFiles.add("menu.xml");
    }
}

• Cascading: A Modest Language Proposal
• Support for operating on a specific instance / Enhanced Builders

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