public class Expression extends Statement
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.
getValue(),
setValue(java.lang.Object)| Constructor and Description |
|---|
Expression(Object value,
Object target,
String methodName,
Object[] arguments)
Creates a new
Expression 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 new
Expression object
for the specified target object to invoke the method
specified by the name and by the array of arguments. |
| Modifier and Type | Method and Description |
|---|---|
void |
execute()
The
execute method finds a method whose name is the same
as the methodName property, and invokes the method on
the target. |
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.
|
void |
setValue(Object value)
Sets the value of this expression to
value. |
String |
toString()
Prints the value of this expression using a Java-style syntax.
|
getArguments, getMethodName, getTarget@ConstructorProperties(value={"target","methodName","arguments"}) public Expression(Object target, String methodName, Object[] arguments)
Expression object
for the specified target object to invoke the method
specified by the name and by the array of arguments.
The target and the methodName values should not be null.
Otherwise an attempt to execute this Expression
will result in a NullPointerException.
If the arguments value is null,
an empty array is used as the value of the arguments property.
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 methodgetValue()public Expression(Object value, Object target, String methodName, Object[] arguments)
Expression object with the specified value
for the specified target object to invoke the method
specified by the name and by the array of arguments.
The value value is used as the value of the value property,
so the getValue() method will return it
without executing this Expression.
The target and the methodName values should not be null.
Otherwise an attempt to execute this Expression
will result in a NullPointerException.
If the arguments value is null,
an empty array is used as the value of the arguments property.
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 methodsetValue(java.lang.Object)public void execute()
throws Exception
execute method finds a method whose name is the same
as the methodName 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 the
Method class itself, conversion between
primitive values and their associated wrapper classes is handled
internally.
The following method types are handled as special cases:
Expressions rather than Statements
as they return a value.
List
interface may also be applied to array instances, mapping to
the static methods of the same name in the Array class.
If the invoked method completes normally,
the value it returns is copied in the value property.
Note that the value property is set to null,
if the return type of the underlying method is void.
execute in class StatementNullPointerException - if the value of the target or
methodName property is nullNoSuchMethodException - if a matching method is not foundSecurityException - if a security manager exists and
it denies the method invocationException - that is thrown by the invoked methodMethodpublic Object getValue() throws Exception
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.
ExceptionStatement.execute(),
setValue(java.lang.Object)public void setValue(Object value)
value.
This value will be returned by the getValue method
without calling the method associated with this
expression.value - The value of this expression.getValue() Submit a bug or feature
For further API reference and developer documentation, see Java SE Documentation. That documentation contains more detailed, developer-targeted descriptions, with conceptual overviews, definitions of terms, workarounds, and working code examples.
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