java.beans: public class: Expression

java.beans
public class: Expression [javadoc | source]

java.lang.Object
   java.beans.Statement
      java.beans.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.

Also see:

getValue

setValue

since: 1.4 -

author: Philip - Milne

Fields inherited from java.beans.Statement:
defaultExceptionListener, loader

Constructor:

Constructor:
public Expression(Object target, String methodName, Object[] arguments) { super(target, methodName, 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 {@code target} and the {@code methodName} values should not be {@code null}. Otherwise an attempt to execute this {@code Expression} will result in a {@code NullPointerException}. If the {@code arguments} value is {@code null}, an empty array is used as the value of the {@code 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 Also see: getValue
public Expression(Object value, Object target, String methodName, Object[] arguments) { this(target, methodName, arguments); setValue(value); } 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 {@code value} value is used as the value of the {@code value} property, so the #getValue method will return it without executing this {@code Expression}. The {@code target} and the {@code methodName} values should not be {@code null}. Otherwise an attempt to execute this {@code Expression} will result in a {@code NullPointerException}. If the {@code arguments} value is {@code null}, an empty array is used as the value of the {@code 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 Also see: setValue

 public Expression(Object target,
    String methodName,
    Object[] arguments) {
        super(target, methodName, arguments);
}

Expression

The {@code target} and the {@code methodName} values should not be {@code null}. Otherwise an attempt to execute this {@code Expression} will result in a {@code NullPointerException}. If the {@code arguments} value is {@code null}, an empty array is used as the value of the {@code 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

Also see:

getValue

 public Expression(Object value,
    Object target,
    String methodName,
    Object[] arguments) {
        this(target, methodName, arguments);
        setValue(value);
}

Expression

#getValue

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

Also see:

setValue

Method from java.beans.Expression Summary:
execute, getValue, instanceName, setValue, toString

Methods from java.beans.Statement:
execute, getArguments, getMethod, getMethodName, getTarget, instanceName, invoke, toString

Methods from java.lang.Object:
clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Method from java.beans.Expression Detail:
public void execute() throws Exception { setValue(invoke()); } {@inheritDoc} If the invoked method completes normally, the value it returns is copied in the {@code value} property. Note that the {@code value} property is set to {@code null}, if the return type of the underlying method is {@code void}.
public Object getValue() throws Exception { if (value == unbound) { setValue(invoke()); } return value; } 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.
String instanceName(Object instance) { return instance == unbound ? "< unbound >" : super.instanceName(instance); }
public void setValue(Object value) { this.value = 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.
public String toString() { return instanceName(value) + "=" + super.toString(); } Prints the value of this expression using a Java-style syntax.

Method from java.beans.Expression Detail:

 public  void execute() throws Exception {
        setValue(invoke());
}

If the invoked method completes normally, the value it returns is copied in the {@code value} property. Note that the {@code value} property is set to {@code null}, if the return type of the underlying method is {@code void}.

 public Object getValue() throws Exception {
        if (value == unbound) {
            setValue(invoke());
        }
        return value;
}

getValue

setValue

getValue

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.

 String instanceName(Object instance) {
        return instance == unbound ? "< unbound >" : super.instanceName(instance);
}

 public  void setValue(Object value) {
        this.value = value;
}

value

 public String toString() {
        return instanceName(value) + "=" + super.toString();
}

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