Class Expression
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.
- Since:
- 1.4
- See Also:
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Constructor Summary
ConstructorDescriptionExpression
(Object value, Object target, String methodName, Object[] arguments) Creates a newExpression
object with the specified value for the specified target object to invoke the method specified by the name and by the array of arguments.Expression
(Object target, String methodName, Object[] arguments) Creates a newExpression
object for the specified target object to invoke the method specified by the name and by the array of arguments. -
Method Summary
Modifier and TypeMethodDescriptionvoid
execute()
Theexecute
method finds a method whose name is the same as themethodName
property, and invokes the method on the target.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.void
Sets the value of this expression tovalue
.toString()
Prints the value of this expression using a Java-style syntax.Methods declared in class java.beans.Statement
getArguments, getMethodName, getTarget
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Constructor Details
-
Expression
@ConstructorProperties({"target","methodName","arguments"}) public Expression(Object target, String methodName, Object[] arguments) Creates a newExpression
object for the specified target object to invoke the method specified by the name and by the array of arguments.The
target
and themethodName
values should not benull
. Otherwise an attempt to execute thisExpression
will result in aNullPointerException
. If thearguments
value isnull
, an empty array is used as the value of thearguments
property.- Parameters:
target
- the target object of this expressionmethodName
- the name of the method to invoke on the specified targetarguments
- the array of arguments to invoke the specified method- See Also:
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Expression
Creates a newExpression
object with the specified value for the specified target object to invoke the method specified by the name and by the array of arguments. Thevalue
value is used as the value of thevalue
property, so thegetValue()
method will return it without executing thisExpression
.The
target
and themethodName
values should not benull
. Otherwise an attempt to execute thisExpression
will result in aNullPointerException
. If thearguments
value isnull
, an empty array is used as the value of thearguments
property.- Parameters:
value
- the value of this expressiontarget
- the target object of this expressionmethodName
- the name of the method to invoke on the specified targetarguments
- the array of arguments to invoke the specified method- See Also:
-
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Method Details
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execute
Theexecute
method finds a method whose name is the same as themethodName
property, and invokes the method on the target. When the target's class defines many methods with the given name the implementation should choose the most specific method using the algorithm specified in the Java Language Specification (15.11). The dynamic class of the target and arguments are used in place of the compile-time type information and, like theMethod
class itself, conversion between primitive values and their associated wrapper classes is handled internally.The following method types are handled as special cases:
- Static methods may be called by using a class object as the target.
-
The reserved method name "new" may be used to call a class's constructor
as if all classes defined static "new" methods. Constructor invocations
are typically considered
Expression
s rather thanStatement
s as they return a value. -
The method names "get" and "set" defined in the
List
interface may also be applied to array instances, mapping to the static methods of the same name in theArray
class.
If the invoked method completes normally, the value it returns is copied in the
value
property. Note that thevalue
property is set tonull
, if the return type of the underlying method isvoid
.- Overrides:
execute
in classStatement
- Throws:
NullPointerException
- if the value of thetarget
ormethodName
property isnull
NoSuchMethodException
- if a matching method is not foundSecurityException
- if a security manager exists and it denies the method invocationException
- that is thrown by the invoked method- Since:
- 1.7
- See Also:
-
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 ofgetValue
. If the value property was already set, either by a call tosetValue
or a previous call togetValue
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 ofnull
replaces this default value in the same way that any other value would, ensuring that expressions are never evaluated more than once.See the
execute
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
- if the method with the specified methodName throws an exception- See Also:
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setValue
Sets the value of this expression tovalue
. 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:
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toString
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