Java 类java.beans.Expression 实例源码

protected Expression instantiate(Object oldInstance, Encoder out)
{
  Class oldClass = (Class) oldInstance;

  // Due to the special handling of String instances in the Encoder
  // this Expression does not lead to further class resolutions.
  if (oldClass == String.class)
    return new Expression(oldClass, "", "getClass", null);

  // This Expression will lead to the class resolution of String.class.
  if (oldClass == Class.class)
    return new Expression(oldClass, String.class, "getClass", null);

  // This Expression will lead to the class resolution of Class.class.
  return new Expression(oldClass, Class.class, "forName",
                        new Object[] { oldClass.getName() });
}

protected Expression instantiate(Object oldInstance, Encoder out)
{
  Class type = oldInstance.getClass().getComponentType();

  // oldInstance is expected to be an array, then
  // getClass().getComponentType() should lead
  // to its component type.
  assert (type != null);

  // Not handling primitive types in a special way here
  // causes that Class.forName("int") is built as an Expression
  // later which would cause an exception if executed. A special
  // handling to avoid the execution for primitive types can be
  // java.beans.Encoder.writeExpression() .
  return new Expression(
                        oldInstance,
                        Array.class,
                        "newInstance",
                        new Object[] {
                          type,
                          new Integer(Array.getLength(oldInstance)) });
}

protected Expression instantiate(Object oldInstance, Encoder out)
{
  Class oldClass = (Class) oldInstance;

  // Due to the special handling of String instances in the Encoder
  // this Expression does not lead to further class resolutions.
  if (oldClass == String.class)
    return new Expression(oldClass, "", "getClass", null);

  // This Expression will lead to the class resolution of String.class.
  if (oldClass == Class.class)
    return new Expression(oldClass, String.class, "getClass", null);

  // This Expression will lead to the class resolution of Class.class. 
  return new Expression(oldClass, Class.class, "forName",
                        new Object[] { oldClass.getName() });
}

protected Expression instantiate(Object oldInstance, Encoder out)
{
  Class type = oldInstance.getClass().getComponentType();

  // oldInstance is expected to be an array, then
  // getClass().getComponentType() should lead
  // to its component type.
  assert (type != null);

  // Not handling primitive types in a special way here
  // causes that Class.forName("int") is built as an Expression
  // later which would cause an exception if executed. A special
  // handling to avoid the execution for primitive types can be
  // java.beans.Encoder.writeExpression() .
  return new Expression(
                        oldInstance,
                        Array.class,
                        "newInstance",
                        new Object[] {
                          type,
                          new Integer(Array.getLength(oldInstance)) });
}

@Override
protected Expression instantiate( Object oldInstance, Encoder out ) {
    Class type = oldInstance.getClass();
    if ( !Modifier.isPublic( type.getModifiers() ) )
        throw new IllegalArgumentException( "Could not instantiate instance of non-public class: " + oldInstance );

    for ( Field field : type.getFields() ) {
        int mod = field.getModifiers();
        if ( Modifier.isPublic( mod ) && Modifier.isStatic( mod ) && Modifier.isFinal( mod ) && ( type == field.getDeclaringClass() ) ) {
            try {
                if ( oldInstance == field.get( null ) )
                    return new Expression( oldInstance, field, "get", new Object[]{null} );
            } catch ( IllegalAccessException exception ) {
                throw new IllegalArgumentException( "Could not get value of the field: " + field, exception );
            }
        }
    }
    throw new IllegalArgumentException( "Could not instantiate value: " + oldInstance );
}

@Test
public void testDiamond() throws Exception {
    if (SourceVersion.latestSupported().ordinal() >= 7) {
        compile("import java.util.List; import java.util.LinkedList; public class A{ List<Integer> bar = new LinkedList<>(); }");
        SymbolTable symTable = getSymbolTable();
        symTable.pushScope();
        SymbolType st = new SymbolType(getClassLoader().loadClass("A"));
        symTable.pushSymbol("a", ReferenceType.VARIABLE, st, null);
        FieldAccessExpr expr = (FieldAccessExpr) ASTManager.parse(Expression.class, "a.bar");
        HashMap<String, Object> ctx = new HashMap<String, Object>();
        expressionAnalyzer.visit(expr, ctx);
        SymbolType type = (SymbolType) expr.getSymbolData();
        Assert.assertNotNull(type);
        Assert.assertEquals("java.util.List", type.getName());
        Assert.assertNotNull(type.getParameterizedTypes());
        Assert.assertEquals("java.lang.Integer", type.getParameterizedTypes().get(0).getName());
    }
}

@Test
public void testTargetInference() throws Exception {

    compile("import java.util.Collections; " + "import java.util.List; "
            + "public class A { public static void processStringList(List<String> stringList) {}}");
    SymbolType st = new SymbolType(getClassLoader().loadClass("A"));
    SymbolTable symTable = getSymbolTable();
    symTable.pushScope();
    symTable.pushSymbol("A", ReferenceType.TYPE, st, null);

    MethodCallExpr expr =
            (MethodCallExpr) ASTManager.parse(Expression.class, "A.processStringList(Collections.emptyList());");
    HashMap<String, Object> ctx = new HashMap<String, Object>();
    expressionAnalyzer.visit(expr, ctx);
    SymbolType type = (SymbolType) expr.getSymbolData();
    Assert.assertNotNull(type);
    Assert.assertEquals("void", type.getName());
}

@Test
public void testLambdaExpressionsWithExplicitArgs() throws Exception {
    if (SourceVersion.latestSupported().ordinal() >= 8) {
        String BCode = "public interface B { public int execute(int c); } ";

        compile("public class A{ public void run(B b){} " + BCode + "}");
        SymbolType st = new SymbolType(getClassLoader().loadClass("A"));
        SymbolTable symTable = getSymbolTable();
        symTable.pushScope();
        symTable.pushSymbol("a", ReferenceType.TYPE, st, null);

        MethodCallExpr expr = (MethodCallExpr) ASTManager.parse(Expression.class, "a.run((int d)->d+1)");
        HashMap<String, Object> ctx = new HashMap<String, Object>();
        expressionAnalyzer.visit(expr, ctx);
        SymbolType type = (SymbolType) expr.getSymbolData();
        Assert.assertNotNull(type);
        Assert.assertEquals("A$B", type.getMethod().getParameterTypes()[0].getName());
    }
}

@Test
public void testMethodReferencesToConstructors() throws Exception {
    if (SourceVersion.latestSupported().ordinal() >= 8) {
        compile("import java.util.HashSet; public class A{ public static void foo(B b) {} public interface B{ public Object get();}}");
        SymbolTable symTable = getSymbolTable();
        symTable.pushSymbol("this", ReferenceType.TYPE, new SymbolType(getClassLoader().loadClass("A")), null);
        MethodCallExpr expr = (MethodCallExpr) ASTManager.parse(Expression.class, "A.foo(HashSet::new)");
        HashMap<String, Object> ctx = new HashMap<String, Object>();
        expressionAnalyzer.visit(expr, ctx);
        SymbolType type = (SymbolType) expr.getSymbolData();
        Assert.assertNotNull(type);
        Assert.assertEquals("foo", type.getMethod().getName());
        MethodReferenceExpr arg1 = (MethodReferenceExpr) expr.getArgs().get(0);

        SymbolType methodType = (SymbolType) arg1.getReferencedMethodSymbolData();
        Assert.assertNotNull(methodType);
        Assert.assertEquals("get", methodType.getMethod().getName());
    }
}

@Test
public void testTargetInferenceShouldFail() throws Exception {

    compile("import java.util.Collections; " + "import java.util.List; "
            + "public class A { public static <T> void processStringList(T[] args) {}}");
    SymbolType st = new SymbolType(getClassLoader().loadClass("A"));
    SymbolTable symTable = getSymbolTable();
    symTable.pushScope();
    symTable.pushSymbol("A", ReferenceType.TYPE, st, null);

    try {
        MethodCallExpr expr = (MethodCallExpr) ASTManager.parse(Expression.class,
                "A.processStringList(Collections.emptyList());");
        HashMap<String, Object> ctx = new HashMap<String, Object>();
        expressionAnalyzer.visit(expr, ctx);
        fail("should not be reached: type=" + expr.getSymbolData().getMethod());
    } catch (NoSuchExpressionTypeException e) {
        Assert.assertTrue(e.getMessage(), e.getMessage()
                .contains("Ops! The method call A.processStringList(Collections.emptyList()) is not resolved"));
    }
}

/**
 * The test checks the correct static method is initialized
 */
public void testStatic() throws Exception {
    SampleBean theBean = new SampleBean();
    Expression expr = new Expression(SampleBean.class, "create",
            new Object[] { "hello", theBean });

    Object result = expr.getValue();
    if (result != null && result instanceof SampleBean) {
        SampleBean bean = (SampleBean) result;
        assertEquals("hello", bean.getText());
        assertEquals(theBean, bean.getObject());
    } else {
        fail("Cannot instantiate an instance of Bean class by "
                + "static method.");
    }
}

@Test
public void testMethodReferencesToAnArrayItem() throws Exception {
    if (SourceVersion.latestSupported().ordinal() >= 8) {
        compile("import java.util.Arrays; public class A{}");
        SymbolType st = new SymbolType(String.class);
        st.setArrayCount(1);
        SymbolTable symTable = getSymbolTable();
        symTable.pushScope();
        symTable.pushSymbol("stringArray", ReferenceType.TYPE, st, null);
        symTable.pushSymbol("this", ReferenceType.TYPE, new SymbolType(getClassLoader().loadClass("A")), null);
        MethodCallExpr expr = (MethodCallExpr) ASTManager.parse(Expression.class,
                "Arrays.sort(stringArray, String::compareToIgnoreCase)");
        HashMap<String, Object> ctx = new HashMap<String, Object>();
        expressionAnalyzer.visit(expr, ctx);
        SymbolType type = (SymbolType) expr.getSymbolData();
        Assert.assertNotNull(type);
        Assert.assertEquals("sort", type.getMethod().getName());
        MethodReferenceExpr arg1 = (MethodReferenceExpr) expr.getArgs().get(1);

        SymbolType methodType = (SymbolType) arg1.getReferencedMethodSymbolData();
        Assert.assertNotNull(methodType);
        Assert.assertEquals("compare", methodType.getMethod().getName());
    }
}

@Test
public void testGenericMethodsExplicitTypeInvocation() throws Exception {
    compile("import java.util.ArrayList; import java.io.Serializable;"
            + " public class A { public static <T> T pick(T a1, T a2) { return a2; }}");
    SymbolTable symTable = getSymbolTable();
    ASTSymbolTypeResolver.getInstance().setSymbolTable(symTable);
    symTable.pushScope();
    SymbolType st = new SymbolType(getClassLoader().loadClass("A"));
    symTable.pushSymbol("A", ReferenceType.TYPE, st, null);

    MethodCallExpr expr = (MethodCallExpr) ASTManager.parse(Expression.class,
            "A.<Serializable>pick(\"d\", new ArrayList<String>())");
    HashMap<String, Object> ctx = new HashMap<String, Object>();
    expressionAnalyzer.visit(expr, ctx);
    SymbolType type = (SymbolType) expr.getSymbolData();
    Assert.assertNotNull(type);
    Assert.assertEquals("java.io.Serializable", type.getName());
}

public void testTargetInference2() throws Exception {

        compile("import java.util.Collections; " + "import java.util.List; "
                + "public class A { public static void processAList(List<A> stringList) {}}");
        SymbolType st = new SymbolType(getClassLoader().loadClass("A"));
        SymbolTable symTable = getSymbolTable();
        symTable.pushScope();
        symTable.pushSymbol("A", ReferenceType.TYPE, st, null);

        MethodCallExpr expr =
                (MethodCallExpr) ASTManager.parse(Expression.class, "A.processAList(Collections.emptyList());");
        HashMap<String, Object> ctx = new HashMap<String, Object>();
        expressionAnalyzer.visit(expr, ctx);
        SymbolType type = (SymbolType) expr.getSymbolData();
        Assert.assertNotNull(type);
        Assert.assertEquals("void", type.getName());
    }

@Test
public void testReferencesToInnerClasses() throws Exception {
    compile(true, "public class OuterClass { public class InnerClass { } }");

    SymbolTable symTable = getSymbolTable();
    ASTSymbolTypeResolver.getInstance().setSymbolTable(symTable);
    symTable.pushScope();
    SymbolType st = new SymbolType(getClassLoader().loadClass("OuterClass"));
    symTable.pushSymbol("outerObject", ReferenceType.VARIABLE, st, null);
    org.walkmod.javalang.ast.expr.Expression expr = (org.walkmod.javalang.ast.expr.Expression) ASTManager
            .parse(Expression.class, "outerObject.new InnerClass()");
    HashMap<String, Object> ctx = new HashMap<String, Object>();
    expr.accept(expressionAnalyzer, ctx);
    SymbolType type = (SymbolType) expr.getSymbolData();
    Assert.assertNotNull(type);
    Assert.assertEquals("OuterClass$InnerClass", type.getName());
}

@Override
protected Expression instantiate(Object oldInstance, Encoder out) {
    byte[] e = (byte[]) oldInstance;
    return new Expression(e, ByteArrayPersistenceDelegate.class,
            "decode",
            new Object[] { ByteArrayPersistenceDelegate.encode(e) });
}

/**
 * Creates the value of this element.
 *
 * @param type  the base class
 * @param args  the array of arguments
 * @return the value of this element
 * @throws Exception if calculation is failed
 */
@Override
protected final ValueObject getValueObject(Class<?> type, Object[] args) throws Exception {
    if (this.field != null) {
        return ValueObjectImpl.create(FieldElementHandler.getFieldValue(getContextBean(), this.field));
    }
    if (this.idref != null) {
        return ValueObjectImpl.create(getVariable(this.idref));
    }
    Object bean = getContextBean();
    String name;
    if (this.index != null) {
        name = (args.length == 2)
                ? PropertyElementHandler.SETTER
                : PropertyElementHandler.GETTER;
    } else if (this.property != null) {
        name = (args.length == 1)
                ? PropertyElementHandler.SETTER
                : PropertyElementHandler.GETTER;

        if (0 < this.property.length()) {
            name += this.property.substring(0, 1).toUpperCase(ENGLISH) + this.property.substring(1);
        }
    } else {
        name = (this.method != null) && (0 < this.method.length())
                ? this.method
                : "new"; // NON-NLS: the constructor marker
    }
    Expression expression = new Expression(bean, name, args);
    return ValueObjectImpl.create(expression.getValue());
}

/**
 * Creates the value of this element.
 *
 * @param type  the base class
 * @param args  the array of arguments
 * @return the value of this element
 * @throws Exception if calculation is failed
 */
@Override
protected final ValueObject getValueObject(Class<?> type, Object[] args) throws Exception {
    if (this.field != null) {
        return ValueObjectImpl.create(FieldElementHandler.getFieldValue(getContextBean(), this.field));
    }
    if (this.idref != null) {
        return ValueObjectImpl.create(getVariable(this.idref));
    }
    Object bean = getContextBean();
    String name;
    if (this.index != null) {
        name = (args.length == 2)
                ? PropertyElementHandler.SETTER
                : PropertyElementHandler.GETTER;
    } else if (this.property != null) {
        name = (args.length == 1)
                ? PropertyElementHandler.SETTER
                : PropertyElementHandler.GETTER;

        if (0 < this.property.length()) {
            name += this.property.substring(0, 1).toUpperCase(ENGLISH) + this.property.substring(1);
        }
    } else {
        name = (this.method != null) && (0 < this.method.length())
                ? this.method
                : "new"; // NON-NLS: the constructor marker
    }
    Expression expression = new Expression(bean, name, args);
    return ValueObjectImpl.create(expression.getValue());
}

public static void main(String[] args) throws Exception {
    Object value = new Object();

    Expression expression = new Expression(value, Object.class, "new", null);
    if (!value.equals(expression.getValue()))
        throw new Error("the value is updated unexpectedly");

    expression.execute();
    if (value.equals(expression.getValue()))
        throw new Error("the value is not updated as expected");
}

@Override
public void writeExpression(Expression expression) {
    if (this.expression == null) {
        this.expression = expression;
    }
    super.writeExpression(expression);
}

protected void initialize(XMLEncoder encoder) {
    encoder.setPersistenceDelegate(Container.class, new PersistenceDelegate() {
        protected Expression instantiate(Object oldInstance, Encoder out) {
            Container container = (Container) oldInstance;
            Component component = container.getComponent();
            return new Expression(container, component, "create", new Object[] {component});
        }
    });
}

protected void initialize(XMLEncoder encoder) {
    encoder.setPersistenceDelegate(
            OuterClass.InnerClass.class,
            new DefaultPersistenceDelegate() {
                protected Expression instantiate(Object oldInstance, Encoder out) {
                    OuterClass.InnerClass inner = (OuterClass.InnerClass) oldInstance;
                    OuterClass outer = inner.getOuter();
                    return new Expression(inner, outer, "getInner", new Object[0]);
                }
            }
    );
}

protected void initialize(XMLEncoder encoder) {
    encoder.setPersistenceDelegate(C.class, new DefaultPersistenceDelegate() {
        protected Expression instantiate(Object oldInstance, Encoder out) {
            C c = (C) oldInstance;
            return new Expression(c, c.getX(), "createC", new Object[] {});
        }
    });
}

/**
 * Creates the value of this element.
 *
 * @param type  the base class
 * @param args  the array of arguments
 * @return the value of this element
 * @throws Exception if calculation is failed
 */
@Override
protected final ValueObject getValueObject(Class<?> type, Object[] args) throws Exception {
    if (this.field != null) {
        return ValueObjectImpl.create(FieldElementHandler.getFieldValue(getContextBean(), this.field));
    }
    if (this.idref != null) {
        return ValueObjectImpl.create(getVariable(this.idref));
    }
    Object bean = getContextBean();
    String name;
    if (this.index != null) {
        name = (args.length == 2)
                ? PropertyElementHandler.SETTER
                : PropertyElementHandler.GETTER;
    } else if (this.property != null) {
        name = (args.length == 1)
                ? PropertyElementHandler.SETTER
                : PropertyElementHandler.GETTER;

        if (0 < this.property.length()) {
            name += this.property.substring(0, 1).toUpperCase(ENGLISH) + this.property.substring(1);
        }
    } else {
        name = (this.method != null) && (0 < this.method.length())
                ? this.method
                : "new"; // NON-NLS: the constructor marker
    }
    Expression expression = new Expression(bean, name, args);
    return ValueObjectImpl.create(expression.getValue());
}

public static void main(String[] args) throws Exception {
    Object value = new Object();

    Expression expression = new Expression(value, Object.class, "new", null);
    if (!value.equals(expression.getValue()))
        throw new Error("the value is updated unexpectedly");

    expression.execute();
    if (value.equals(expression.getValue()))
        throw new Error("the value is not updated as expected");
}

@Override
public void writeExpression(Expression expression) {
    if (this.expression == null) {
        this.expression = expression;
    }
    super.writeExpression(expression);
}

protected void initialize(XMLEncoder encoder) {
    encoder.setPersistenceDelegate(Container.class, new PersistenceDelegate() {
        protected Expression instantiate(Object oldInstance, Encoder out) {
            Container container = (Container) oldInstance;
            Component component = container.getComponent();
            return new Expression(container, component, "create", new Object[] {component});
        }
    });
}

protected void initialize(XMLEncoder encoder) {
    encoder.setPersistenceDelegate(
            OuterClass.InnerClass.class,
            new DefaultPersistenceDelegate() {
                protected Expression instantiate(Object oldInstance, Encoder out) {
                    OuterClass.InnerClass inner = (OuterClass.InnerClass) oldInstance;
                    OuterClass outer = inner.getOuter();
                    return new Expression(inner, outer, "getInner", new Object[0]);
                }
            }
    );
}

protected void initialize(XMLEncoder encoder) {
    encoder.setPersistenceDelegate(C.class, new DefaultPersistenceDelegate() {
        protected Expression instantiate(Object oldInstance, Encoder out) {
            C c = (C) oldInstance;
            return new Expression(c, c.getX(), "createC", new Object[] {});
        }
    });
}

/**
 * Creates the value of this element.
 *
 * @param type  the base class
 * @param args  the array of arguments
 * @return the value of this element
 * @throws Exception if calculation is failed
 */
@Override
protected final ValueObject getValueObject(Class<?> type, Object[] args) throws Exception {
    if (this.field != null) {
        return ValueObjectImpl.create(FieldElementHandler.getFieldValue(getContextBean(), this.field));
    }
    if (this.idref != null) {
        return ValueObjectImpl.create(getVariable(this.idref));
    }
    Object bean = getContextBean();
    String name;
    if (this.index != null) {
        name = (args.length == 2)
                ? PropertyElementHandler.SETTER
                : PropertyElementHandler.GETTER;
    } else if (this.property != null) {
        name = (args.length == 1)
                ? PropertyElementHandler.SETTER
                : PropertyElementHandler.GETTER;

        if (0 < this.property.length()) {
            name += this.property.substring(0, 1).toUpperCase(ENGLISH) + this.property.substring(1);
        }
    } else {
        name = (this.method != null) && (0 < this.method.length())
                ? this.method
                : "new"; // NON-NLS: the constructor marker
    }
    Expression expression = new Expression(bean, name, args);
    return ValueObjectImpl.create(expression.getValue());
}

public static void main(String[] args) throws Exception {
    Object value = new Object();

    Expression expression = new Expression(value, Object.class, "new", null);
    if (!value.equals(expression.getValue()))
        throw new Error("the value is updated unexpectedly");

    expression.execute();
    if (value.equals(expression.getValue()))
        throw new Error("the value is not updated as expected");
}

@Override
public void writeExpression(Expression expression) {
    if (this.expression == null) {
        this.expression = expression;
    }
    super.writeExpression(expression);
}

protected void initialize(XMLEncoder encoder) {
    encoder.setPersistenceDelegate(Container.class, new PersistenceDelegate() {
        protected Expression instantiate(Object oldInstance, Encoder out) {
            Container container = (Container) oldInstance;
            Component component = container.getComponent();
            return new Expression(container, component, "create", new Object[] {component});
        }
    });
}

protected void initialize(XMLEncoder encoder) {
    encoder.setPersistenceDelegate(
            OuterClass.InnerClass.class,
            new DefaultPersistenceDelegate() {
                protected Expression instantiate(Object oldInstance, Encoder out) {
                    OuterClass.InnerClass inner = (OuterClass.InnerClass) oldInstance;
                    OuterClass outer = inner.getOuter();
                    return new Expression(inner, outer, "getInner", new Object[0]);
                }
            }
    );
}

protected void initialize(XMLEncoder encoder) {
    encoder.setPersistenceDelegate(C.class, new DefaultPersistenceDelegate() {
        protected Expression instantiate(Object oldInstance, Encoder out) {
            C c = (C) oldInstance;
            return new Expression(c, c.getX(), "createC", new Object[] {});
        }
    });
}

@SuppressWarnings("unchecked")
public static <E,R> R getMethodValue(E obj, Method method, Object... args) {
    R value = null;

    try {
        method.setAccessible(true);

        value = (R) method.invoke(obj, args);
    } catch (InvocationTargetException | IllegalAccessException | IllegalArgumentException e) {
        // e.printStackTrace();
        try {
            if (obj != null) {
                Expression expr = new Expression(obj, method.getName(), args);
                expr.execute();
                value = (R) expr.getValue();
            }

            if (value == null) {
                value = (R) method.getDefaultValue();
            }

        } catch (Exception e1) {
            // e1.printStackTrace();
        }
    }

    return value;
}

/**
 * Creates the value of this element.
 *
 * @param type  the base class
 * @param args  the array of arguments
 * @return the value of this element
 * @throws Exception if calculation is failed
 */
@Override
protected final ValueObject getValueObject(Class<?> type, Object[] args) throws Exception {
    if (this.field != null) {
        return ValueObjectImpl.create(FieldElementHandler.getFieldValue(getContextBean(), this.field));
    }
    if (this.idref != null) {
        return ValueObjectImpl.create(getVariable(this.idref));
    }
    Object bean = getContextBean();
    String name;
    if (this.index != null) {
        name = (args.length == 2)
                ? PropertyElementHandler.SETTER
                : PropertyElementHandler.GETTER;
    } else if (this.property != null) {
        name = (args.length == 1)
                ? PropertyElementHandler.SETTER
                : PropertyElementHandler.GETTER;

        if (0 < this.property.length()) {
            name += this.property.substring(0, 1).toUpperCase(ENGLISH) + this.property.substring(1);
        }
    } else {
        name = (this.method != null) && (0 < this.method.length())
                ? this.method
                : "new"; // NON-NLS: the constructor marker
    }
    Expression expression = new Expression(bean, name, args);
    return ValueObjectImpl.create(expression.getValue());
}

public static void main(String[] args) throws Exception {
    Object value = new Object();

    Expression expression = new Expression(value, Object.class, "new", null);
    if (!value.equals(expression.getValue()))
        throw new Error("the value is updated unexpectedly");

    expression.execute();
    if (value.equals(expression.getValue()))
        throw new Error("the value is not updated as expected");
}

@Override
public void writeExpression(Expression expression) {
    if (this.expression == null) {
        this.expression = expression;
    }
    super.writeExpression(expression);
}

protected void initialize(XMLEncoder encoder) {
    encoder.setPersistenceDelegate(Container.class, new PersistenceDelegate() {
        protected Expression instantiate(Object oldInstance, Encoder out) {
            Container container = (Container) oldInstance;
            Component component = container.getComponent();
            return new Expression(container, component, "create", new Object[] {component});
        }
    });
}