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.
Constructor | Description |
---|---|
Expression |
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 |
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 | 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 |
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({"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 methodpublic 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 methodpublic 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:
Expression
s rather than Statement
s 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 Statement
NullPointerException
- if the value of the target
or methodName
property is null
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 methodpublic 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 execute
method for details on how methods are chosen using the dynamic types of the target and arguments.
Exception
- if the method with the specified methodName throws an exceptionpublic 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.public String toString()
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https://docs.oracle.com/en/java/javase/21/docs/api/java.desktop/java/beans/Expression.html