Class Expression
- java.lang.Object
-
- java.beans.Statement
-
- java.beans.Expression
public class Expression extends Statement
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.
- Since:
- 1.4
- See Also:
-
getValue()
,setValue(java.lang.Object)
Constructor Summary
Constructor | Description |
---|---|
Expression(Object value,
Object target,
String methodName,
Object[] arguments) | Creates a new |
Expression(Object target,
String methodName,
Object[] arguments) | Creates a new |
Method Summary
Modifier and Type | Method | Description |
---|---|---|
void | execute() | The |
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 |
String | toString() | Prints the value of this expression using a Java-style syntax. |
Methods declared in class java.beans.Statement
getArguments, getMethodName, getTarget
Methods declared in class java.lang.Object
clone, equals, finalize, getClass, hashCode, notify, notifyAll, wait, wait, wait
Constructor Detail
Expression
@ConstructorProperties({"target","methodName","arguments"}) public 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.
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.
- Parameters:
-
target
- the target object of this expression -
methodName
- the name of the method to invoke on the specified target -
arguments
- the array of arguments to invoke the specified method - See Also:
getValue()
Expression
public 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. 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.
- Parameters:
-
value
- the value of this expression -
target
- the target object of this expression -
methodName
- the name of the method to invoke on the specified target -
arguments
- the array of arguments to invoke the specified method - See Also:
setValue(java.lang.Object)
Method Detail
execute
public void execute() throws Exception
The 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:
- 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 the value
property is set to null
, if the return type of the underlying method is void
.
- Overrides:
-
execute
in classStatement
- Throws:
-
NullPointerException
- if the value of thetarget
ormethodName
property isnull
-
NoSuchMethodException
- if a matching method is not found -
SecurityException
- if a security manager exists and it denies the method invocation -
Exception
- that is thrown by the invoked method - Since:
- 1.7
- See Also:
Method
getValue
public Object getValue() throws Exception
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 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:
-
Statement.execute()
,setValue(java.lang.Object)
setValue
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:
getValue()
toString
public String toString()
Prints the value of this expression using a Java-style syntax.