Initial revision

From-SVN: r102074

libjava/classpath/java/beans/Expression.java

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+/* java.beans.Expression
+   Copyright (C) 2004 Free Software Foundation, Inc.
+
+This file is part of GNU Classpath.
+
+GNU Classpath is free software; you can redistribute it and/or modify
+it under the terms of the GNU General Public License as published by
+the Free Software Foundation; either version 2, or (at your option)
+any later version.
+ 
+GNU Classpath is distributed in the hope that it will be useful, but
+WITHOUT ANY WARRANTY; without even the implied warranty of
+MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+General Public License for more details.
+
+You should have received a copy of the GNU General Public License
+along with GNU Classpath; see the file COPYING.  If not, write to the
+Free Software Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA
+02110-1301 USA.
+
+Linking this library statically or dynamically with other modules is
+making a combined work based on this library.  Thus, the terms and
+conditions of the GNU General Public License cover the whole
+combination.
+
+As a special exception, the copyright holders of this library give you
+permission to link this library with independent modules to produce an
+executable, regardless of the license terms of these independent
+modules, and to copy and distribute the resulting executable under
+terms of your choice, provided that you also meet, for each linked
+independent module, the terms and conditions of the license of that
+module.  An independent module is a module which is not derived from
+or based on this library.  If you modify this library, you may extend
+this exception to your version of the library, but you are not
+obligated to do so.  If you do not wish to do so, delete this
+exception statement from your version. */
+
+
+package java.beans;
+
+/**
+ * class Expression
+ *
+ * An Expression captures the execution of an object method that
+ * returns a value.  It stores an object, the method to call, and the
+ * arguments to pass to the method.
+ *
+ * @since 1.4
+ */
+public class Expression extends Statement
+{
+  // This is a placeholder to indicate that value hasn't been set
+  // yet;
+  private static final Object unset = new Object();
+
+  // The value to return.  This is equal to unset until getValue is called.
+  private Object value;
+   
+
+  /**
+   * Constructor
+   *
+   * Constructs an Expression representing the invocation of
+   * object.methodName(arg[0], arg[1], ...);  However, it will never
+   * be executed.  Instead, value will always be returned.
+   *
+   * @param value The value to return.
+   * @param target The object to invoke the method on.
+   * @param methodName The object method to invoke.
+   * @param arguments An array of arguments to pass to the method.
+   */
+  public Expression(Object value, Object target, String methodName,
+		    Object[] arguments)
+  {
+    super(target, methodName, arguments);
+    this.value = value;
+  }
+
+  /**
+   * Constructor
+   *
+   * Constructs an Expression representing the invocation of
+   * object.methodName(arg[0], arg[1], ...);
+   *
+   * @param target The object to invoke the method on.
+   * @param methodName The object method to invoke.
+   * @param arguments An array of arguments to pass to the method.
+   */
+  public Expression(Object target, String methodName, Object[] arguments)
+  {
+    super(target, methodName, arguments);
+    this.value = unset;
+  }
+
+  /**
+   * Return the result of executing the method.
+   *
+   * If the cached value has not yet been set, the method is
+   * executed in the same way as Statement.execute(), except that
+   * the value is cached, and then returned.  If the value has been
+   * set, it is returned without executing the method again.
+   *
+   * @return the result of executing the method.
+   * @exception Exception if an error occurs
+   */
+  public Object getValue() throws Exception
+  {
+    if (value == unset)
+      value = doExecute();
+    return value;
+  }
+
+  /**
+   * Set the cached value to be returned by getValue()
+   *
+   * @param value the value to cache and return.
+   */
+  public void setValue(Object value)
+  {
+    this.value = value;
+  }
+    
+  /**
+   * Return a string representation of this expression.
+   */
+  public String toString()
+  {
+    String result = super.toString();
+    if (value != unset)
+      return value.getClass().getName() + " " + result;
+    return result;
+  }
+}