| java.lang.Object | ||
| ↳ | java.beans.Statement | |
| ↳ | java.beans.Expression | |
Class Overview
An Expression object represents a primitive expression
in which a single method is applied to a target and a set of
arguments to return a result - as in "a.getFoo()".
In addition to the properties of the super class, the
Expression object provides a value which
is the object returned when this expression is evaluated.
The return value is typically not provided by the caller and
is instead computed by dynamically finding the method and invoking
it when the first call to getValue is made.
See Also
Summary
| Public Constructors | |||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|
Creates a new
Statement object with a target,
methodName and arguments as per the parameters. | |||||||||||
Creates a new
Expression object for a method
that returns a result. | |||||||||||
| Public Methods | |||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|
If the value property of this instance is not already set,
this method dynamically finds the method with the specified
methodName on this target with these arguments and calls it.
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Sets the value of this expression to
value. | |||||||||||
Prints the value of this expression using a Java-style syntax.
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Inherited Methods | |||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|
From class
java.beans.Statement
| |||||||||||
|
From class
java.lang.Object
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Public Constructors
public Expression (Object target, String methodName, Object[] arguments)
Creates a new Statement object with a target,
methodName and arguments as per the parameters.
Parameters
| target | The target of this expression. |
|---|---|
| methodName | The methodName of this expression. |
| arguments | The arguments of this expression. If null then an empty array will be used. |
See Also
public Expression (Object value, Object target, String methodName, Object[] arguments)
Creates a new Expression object for a method
that returns a result. The result will never be calculated
however, since this constructor uses the value
parameter to set the value property by calling the
setValue method.
Parameters
| value | The value of this expression. |
|---|---|
| target | The target of this expression. |
| methodName | The methodName of this expression. |
| arguments | The arguments of this expression. If null then an empty array will be used. |
See Also
Public Methods
public Object getValue ()
If the value property of this instance is not already set,
this method dynamically finds the method with the specified
methodName on this target with these arguments and calls it.
The result of the method invocation is first copied
into the value property of this expression and then returned
as the result of getValue. If the value property
was already set, either by a call to setValue
or a previous call to getValue then the value
property is returned without either looking up or calling the method.
The value property of an Expression is set to
a unique private (non-null) value by default and
this value is used as an internal indication that the method
has not yet been called. A return value of null
replaces this default value in the same way that any other value
would, ensuring that expressions are never evaluated more than once.
See the excecute method for details on how
methods are chosen using the dynamic types of the target
and arguments.
Returns
- The result of applying this method to these arguments.
Throws
| Exception |
|---|
See Also
public void setValue (Object value)
Sets the value of this expression to value.
This value will be returned by the getValue method
without calling the method associated with this
expression.
Parameters
| value | The value of this expression. |
|---|
See Also
public String toString ()
Prints the value of this expression using a Java-style syntax.
Returns
- a string representation of the object.