Expression JDK 1.6)

Description

public class Expression

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: Expression.getValue() Expression.setValue(java.lang.Object)

Constructors

public Expression (Object value, Object target, String methodName, Object arguments)

Creates a new Expression object for a method that returns a result.

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: Expression.setValue(java.lang.Object),

public Expression (Object target, String methodName, Object arguments)

Creates a new Statement object with a target, methodName and arguments as per the parameters.

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: Expression.getValue(),

Methods

Hide/Show inherited methods

public void execute () throws Exception [Inherited From Statement]

The execute method finds a method whose name is the same as the methodName property, and invokes the method on the target.

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 java.lang.reflect.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 Expressions rather than Statements as they return a value.
The method names "get" and "set" defined in the java.util.List interface may also be applied to array instances, mapping to the static methods of the same name in the Array class.

public Object getArguments () [Inherited From Statement]

Returns the arguments of this statement.

public String getMethodName () [Inherited From Statement]

Returns the name of the method.

public Object getTarget () [Inherited From Statement]

Returns the target of this statement.

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.

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.
See Also: Statement.execute(), Expression.setValue(java.lang.Object),

pack-private String instanceName (Object instance) [Overrides Statement]

pack-private Object invoke () throws Exception [Inherited From Statement]

public void setValue (Object value)

Sets the value of this expression to 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: Expression.getValue(),

public String toString () [Overrides Statement]

Prints the value of this expression using a Java-style syntax.