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Static class declarations
Can a class -- inner or outer -- be declared static?
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If your main class has a few smaller helper classes that can be used outside the class and make sense only with your main
class, it's a good idea to make them nested top-level classes. To use the nested top-level class, write: TopLevelClass.NestedClass.
See the following example:
public class Filter {
Vector criteria = new Vector();
public addCriterion(Criterion c) {
criteria.addElement(c);
}
public boolean isTrue(Record rec) {
for(Enumeration e=criteria.elements();
e.hasMoreElements();) {
if(! ((Criterion)e.nextElement()).isTrue(rec))
return false;
}
return true;
}
public static class Criterion {
String colName, colValue;
public Criterion(Stirng name, String val) {
colName = name; colValue = val;
}
public boolean isTrue(Record rec) {
String data = rec.getData(colName);
if(data.equals(colValue)) return true;
return false;
}
}
}
And when you want to use it:
Filter f = new Filter();
f.addCriterion(new Filter.Criterion("SYMBOL", "SUNW"));
f.addCriterion(new Filter.Criterion("SIDE", "BUY"));
.....
if(f.isTrue(someRec)) //do some thing .....
One important note: The static keyword does not do to a class declaration what it does to a variable or a method declaration.
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Resources
- "Java Tip 75Use nested classes for better organization," Ramnivas Laddad (JavaWorld, August 1999). This tip examines nested top-level classes in detail, including code examples
http://www.javaworld.com/javaworld/javatips/jw-javatip75.html - The complete source code for Java Tip 75 is available in zip format. The source code files are divided into
/beforeand/afterdirectories, corresponding to the nonnested and nested examples provided
http://www.javaworld.com/javatips/javatip75/jw-javatip75.zip - The class documentation for Java Tip 75's nonnested class example
http://www.javaworld.com/javaworld/javatips/javatip75/before/docs/index.html - The class documentation for Java Tip 75's nested class example
http://www.javaworld.com/javaworld/javatips/javatip75/after/docs/index.html - Sun's Java Language Specification regarding inner types
http://java.sun.com/products/jdk/1.1/docs/guide/innerclasses/spec/innerclasses.doc.html - MVC in Swing
http://java.sun.com/products/jfc/tsc/what_is_swing/getting_started_2/getting_started_2.html - Design PatternsElements of Reusable Object-Oriented Software, Erich Gamma, Richard Helm, Ralph Johnson, and John Vlissides -- the "Gang of Four" (Addison Wesley, 1994)
http://www1.fatbrain.com/asp/bookinfo/bookinfo.asp?theisbn=0201633612
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Inner class object creation in mainBy Anonymous on November 16, 2009, 2:44 pmIs it necessary to declare an inner class as static if we want to create its object in main which is in same outer class??
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No ref to parentBy Anonymous on October 20, 2009, 4:03 amYou could declare all the inner classes without a reference to the parent object to be static inner classes.
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static classBy Anonymous on September 19, 2009, 11:15 pmIs that required create an instance to static class explicitly....?
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shall we have all static methods in class then wht we call that By Anonymous on August 21, 2009, 1:39 amShall we have all static methods in a class then what is that class called ? could you please explain me
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Was of great help to me, in understanding why the inner classes By Anonymous on August 17, 2009, 11:18 amWas of great help to me, in understanding why the inner classes are declared static. Thanks
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