/*
 * Copyright 2002-2017 the original author or authors.
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *      https://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
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package org.springframework.expression;

import org.springframework.core.convert.TypeDescriptor;
import org.springframework.lang.Nullable;

An expression capable of evaluating itself against context objects.
Encapsulates the details of a previously parsed expression string.
Provides a common abstraction for expression evaluation.
Author:
Keith Donald, Andy Clement, Juergen Hoeller
Since:
3.0/**
 * An expression capable of evaluating itself against context objects.
 * Encapsulates the details of a previously parsed expression string.
 * Provides a common abstraction for expression evaluation.
 *
 * @author Keith Donald
 * @author Andy Clement
 * @author Juergen Hoeller
 * @since 3.0
 */
public interface Expression {

	
Return the original string used to create this expression (unmodified).
Returns:
the original expression string/**
	 * Return the original string used to create this expression (unmodified).
	 * @return the original expression string
	 */
	String getExpressionString();

	
Evaluate this expression in the default standard context.
Throws:
EvaluationException – if there is a problem during evaluation
Returns:
the evaluation result/**
	 * Evaluate this expression in the default standard context.
	 * @return the evaluation result
	 * @throws EvaluationException if there is a problem during evaluation
	 */
	@Nullable
	Object getValue() throws EvaluationException;

	
Evaluate the expression in the default context. If the result
of the evaluation does not match (and cannot be converted to)
the expected result type then an exception will be returned.
Params:
desiredResultType – the class the caller would like the result to be
Throws:
EvaluationException – if there is a problem during evaluation
Returns:
the evaluation result/**
	 * Evaluate the expression in the default context. If the result
	 * of the evaluation does not match (and cannot be converted to)
	 * the expected result type then an exception will be returned.
	 * @param desiredResultType the class the caller would like the result to be
	 * @return the evaluation result
	 * @throws EvaluationException if there is a problem during evaluation
	 */
	@Nullable
	<T> T getValue(@Nullable Class<T> desiredResultType) throws EvaluationException;

	
Evaluate this expression against the specified root object.
Params:
rootObject – the root object against which to evaluate the expression
Throws:
EvaluationException – if there is a problem during evaluation
Returns:
the evaluation result/**
	 * Evaluate this expression against the specified root object.
	 * @param rootObject the root object against which to evaluate the expression
	 * @return the evaluation result
	 * @throws EvaluationException if there is a problem during evaluation
	 */
	@Nullable
	Object getValue(@Nullable Object rootObject) throws EvaluationException;

	
Evaluate the expression in the default context against the specified root
object. If the result of the evaluation does not match (and cannot be
converted to) the expected result type then an exception will be returned.
Params:
rootObject – the root object against which to evaluate the expression
desiredResultType – the class the caller would like the result to be
Throws:
EvaluationException – if there is a problem during evaluation
Returns:
the evaluation result/**
	 * Evaluate the expression in the default context against the specified root
	 * object. If the result of the evaluation does not match (and cannot be
	 * converted to) the expected result type then an exception will be returned.
	 * @param rootObject the root object against which to evaluate the expression
	 * @param desiredResultType the class the caller would like the result to be
	 * @return the evaluation result
	 * @throws EvaluationException if there is a problem during evaluation
	 */
	@Nullable
	<T> T getValue(@Nullable Object rootObject, @Nullable Class<T> desiredResultType) throws EvaluationException;

	
Evaluate this expression in the provided context and return the result
of evaluation.
Params:
context – the context in which to evaluate the expression
Throws:
EvaluationException – if there is a problem during evaluation
Returns:
the evaluation result/**
	 * Evaluate this expression in the provided context and return the result
	 * of evaluation.
	 * @param context the context in which to evaluate the expression
	 * @return the evaluation result
	 * @throws EvaluationException if there is a problem during evaluation
	 */
	@Nullable
	Object getValue(EvaluationContext context) throws EvaluationException;

	
Evaluate this expression in the provided context and return the result
of evaluation, but use the supplied root context as an override for any
default root object specified in the context.
Params:
context – the context in which to evaluate the expression
rootObject – the root object against which to evaluate the expression
Throws:
EvaluationException – if there is a problem during evaluation
Returns:
the evaluation result/**
	 * Evaluate this expression in the provided context and return the result
	 * of evaluation, but use the supplied root context as an override for any
	 * default root object specified in the context.
	 * @param context the context in which to evaluate the expression
	 * @param rootObject the root object against which to evaluate the expression
	 * @return the evaluation result
	 * @throws EvaluationException if there is a problem during evaluation
	 */
	@Nullable
	Object getValue(EvaluationContext context, @Nullable Object rootObject) throws EvaluationException;

	
Evaluate the expression in a specified context which can resolve references
to properties, methods, types, etc. The type of the evaluation result is
expected to be of a particular class and an exception will be thrown if it
is not and cannot be converted to that type.
Params:
context – the context in which to evaluate the expression
desiredResultType – the class the caller would like the result to be
Throws:
EvaluationException – if there is a problem during evaluation
Returns:
the evaluation result/**
	 * Evaluate the expression in a specified context which can resolve references
	 * to properties, methods, types, etc. The type of the evaluation result is
	 * expected to be of a particular class and an exception will be thrown if it
	 * is not and cannot be converted to that type.
	 * @param context the context in which to evaluate the expression
	 * @param desiredResultType the class the caller would like the result to be
	 * @return the evaluation result
	 * @throws EvaluationException if there is a problem during evaluation
	 */
	@Nullable
	<T> T getValue(EvaluationContext context, @Nullable Class<T> desiredResultType) throws EvaluationException;

	
Evaluate the expression in a specified context which can resolve references
to properties, methods, types, etc. The type of the evaluation result is
expected to be of a particular class and an exception will be thrown if it
is not and cannot be converted to that type. The supplied root object
overrides any default specified on the supplied context.
Params:
context – the context in which to evaluate the expression
rootObject – the root object against which to evaluate the expression
desiredResultType – the class the caller would like the result to be
Throws:
EvaluationException – if there is a problem during evaluation
Returns:
the evaluation result/**
	 * Evaluate the expression in a specified context which can resolve references
	 * to properties, methods, types, etc. The type of the evaluation result is
	 * expected to be of a particular class and an exception will be thrown if it
	 * is not and cannot be converted to that type. The supplied root object
	 * overrides any default specified on the supplied context.
	 * @param context the context in which to evaluate the expression
	 * @param rootObject the root object against which to evaluate the expression
	 * @param desiredResultType the class the caller would like the result to be
	 * @return the evaluation result
	 * @throws EvaluationException if there is a problem during evaluation
	 */
	@Nullable
	<T> T getValue(EvaluationContext context, @Nullable Object rootObject, @Nullable Class<T> desiredResultType)
			throws EvaluationException;

	
Return the most general type that can be passed to a setValue method using the default context. 
Throws:
EvaluationException – if there is a problem determining the type
Returns:
the most general type of value that can be set on this context/**
	 * Return the most general type that can be passed to a {@link #setValue}
	 * method using the default context.
	 * @return the most general type of value that can be set on this context
	 * @throws EvaluationException if there is a problem determining the type
	 */
	@Nullable
	Class<?> getValueType() throws EvaluationException;

	
Return the most general type that can be passed to the setValue(Object, Object) method using the default context. 
Params:
rootObject – the root object against which to evaluate the expression
Throws:
EvaluationException – if there is a problem determining the type
Returns:
the most general type of value that can be set on this context/**
	 * Return the most general type that can be passed to the
	 * {@link #setValue(Object, Object)} method using the default context.
	 * @param rootObject the root object against which to evaluate the expression
	 * @return the most general type of value that can be set on this context
	 * @throws EvaluationException if there is a problem determining the type
	 */
	@Nullable
	Class<?> getValueType(@Nullable Object rootObject) throws EvaluationException;

	
Return the most general type that can be passed to the setValue(EvaluationContext, Object) method for the given context. 
Params:
context – the context in which to evaluate the expression
Throws:
EvaluationException – if there is a problem determining the type
Returns:
the most general type of value that can be set on this context/**
	 * Return the most general type that can be passed to the
	 * {@link #setValue(EvaluationContext, Object)} method for the given context.
	 * @param context the context in which to evaluate the expression
	 * @return the most general type of value that can be set on this context
	 * @throws EvaluationException if there is a problem determining the type
	 */
	@Nullable
	Class<?> getValueType(EvaluationContext context) throws EvaluationException;

	
Return the most general type that can be passed to the setValue(EvaluationContext, Object, Object) method for the given context. The supplied root object overrides any specified in the context. 
Params:
context – the context in which to evaluate the expression
rootObject – the root object against which to evaluate the expression
Throws:
EvaluationException – if there is a problem determining the type
Returns:
the most general type of value that can be set on this context/**
	 * Return the most general type that can be passed to the
	 * {@link #setValue(EvaluationContext, Object, Object)} method for the given
	 * context. The supplied root object overrides any specified in the context.
	 * @param context the context in which to evaluate the expression
	 * @param rootObject the root object against which to evaluate the expression
	 * @return the most general type of value that can be set on this context
	 * @throws EvaluationException if there is a problem determining the type
	 */
	@Nullable
	Class<?> getValueType(EvaluationContext context, @Nullable Object rootObject) throws EvaluationException;

	
Return the most general type that can be passed to a setValue method using the default context. 
Throws:
EvaluationException – if there is a problem determining the type
Returns:
a type descriptor for values that can be set on this context/**
	 * Return the most general type that can be passed to a {@link #setValue}
	 * method using the default context.
	 * @return a type descriptor for values that can be set on this context
	 * @throws EvaluationException if there is a problem determining the type
	 */
	@Nullable
	TypeDescriptor getValueTypeDescriptor() throws EvaluationException;

	
Return the most general type that can be passed to the setValue(Object, Object) method using the default context. 
Params:
rootObject – the root object against which to evaluate the expression
Throws:
EvaluationException – if there is a problem determining the type
Returns:
a type descriptor for values that can be set on this context/**
	 * Return the most general type that can be passed to the
	 * {@link #setValue(Object, Object)} method using the default context.
	 * @param rootObject the root object against which to evaluate the expression
	 * @return a type descriptor for values that can be set on this context
	 * @throws EvaluationException if there is a problem determining the type
	 */
	@Nullable
	TypeDescriptor getValueTypeDescriptor(@Nullable Object rootObject) throws EvaluationException;

	
Return the most general type that can be passed to the setValue(EvaluationContext, Object) method for the given context. 
Params:
context – the context in which to evaluate the expression
Throws:
EvaluationException – if there is a problem determining the type
Returns:
a type descriptor for values that can be set on this context/**
	 * Return the most general type that can be passed to the
	 * {@link #setValue(EvaluationContext, Object)} method for the given context.
	 * @param context the context in which to evaluate the expression
	 * @return a type descriptor for values that can be set on this context
	 * @throws EvaluationException if there is a problem determining the type
	 */
	@Nullable
	TypeDescriptor getValueTypeDescriptor(EvaluationContext context) throws EvaluationException;

	
Return the most general type that can be passed to the setValue(EvaluationContext, Object, Object) method for the given context. The supplied root object overrides any specified in the context. 
Params:
context – the context in which to evaluate the expression
rootObject – the root object against which to evaluate the expression
Throws:
EvaluationException – if there is a problem determining the type
Returns:
a type descriptor for values that can be set on this context/**
	 * Return the most general type that can be passed to the
	 * {@link #setValue(EvaluationContext, Object, Object)} method for the given
	 * context. The supplied root object overrides any specified in the context.
	 * @param context the context in which to evaluate the expression
	 * @param rootObject the root object against which to evaluate the expression
	 * @return a type descriptor for values that can be set on this context
	 * @throws EvaluationException if there is a problem determining the type
	 */
	@Nullable
	TypeDescriptor getValueTypeDescriptor(EvaluationContext context, @Nullable Object rootObject) throws EvaluationException;

	
Determine if an expression can be written to, i.e. setValue() can be called.
Params:
rootObject – the root object against which to evaluate the expression
Throws:
EvaluationException – if there is a problem determining if it is writable
Returns:
true if the expression is writable; false otherwise/**
	 * Determine if an expression can be written to, i.e. setValue() can be called.
	 * @param rootObject the root object against which to evaluate the expression
	 * @return {@code true} if the expression is writable; {@code false} otherwise
	 * @throws EvaluationException if there is a problem determining if it is writable
	 */
	boolean isWritable(@Nullable Object rootObject) throws EvaluationException;

	
Determine if an expression can be written to, i.e. setValue() can be called.
Params:
context – the context in which the expression should be checked
Throws:
EvaluationException – if there is a problem determining if it is writable
Returns:
true if the expression is writable; false otherwise/**
	 * Determine if an expression can be written to, i.e. setValue() can be called.
	 * @param context the context in which the expression should be checked
	 * @return {@code true} if the expression is writable; {@code false} otherwise
	 * @throws EvaluationException if there is a problem determining if it is writable
	 */
	boolean isWritable(EvaluationContext context) throws EvaluationException;

	
Determine if an expression can be written to, i.e. setValue() can be called.
The supplied root object overrides any specified in the context.
Params:
context – the context in which the expression should be checked
rootObject – the root object against which to evaluate the expression
Throws:
EvaluationException – if there is a problem determining if it is writable
Returns:
true if the expression is writable; false otherwise/**
	 * Determine if an expression can be written to, i.e. setValue() can be called.
	 * The supplied root object overrides any specified in the context.
	 * @param context the context in which the expression should be checked
	 * @param rootObject the root object against which to evaluate the expression
	 * @return {@code true} if the expression is writable; {@code false} otherwise
	 * @throws EvaluationException if there is a problem determining if it is writable
	 */
	boolean isWritable(EvaluationContext context, @Nullable Object rootObject) throws EvaluationException;

	
Set this expression in the provided context to the value provided.
Params:
rootObject – the root object against which to evaluate the expression
value – the new value
Throws:
EvaluationException – if there is a problem during evaluation/**
	 * Set this expression in the provided context to the value provided.
	 * @param rootObject the root object against which to evaluate the expression
	 * @param value the new value
	 * @throws EvaluationException if there is a problem during evaluation
	 */
	void setValue(@Nullable Object rootObject, @Nullable Object value) throws EvaluationException;

	
Set this expression in the provided context to the value provided.
Params:
context – the context in which to set the value of the expression
value – the new value
Throws:
EvaluationException – if there is a problem during evaluation/**
	 * Set this expression in the provided context to the value provided.
	 * @param context the context in which to set the value of the expression
	 * @param value the new value
	 * @throws EvaluationException if there is a problem during evaluation
	 */
	void setValue(EvaluationContext context, @Nullable Object value) throws EvaluationException;

	
Set this expression in the provided context to the value provided.
The supplied root object overrides any specified in the context.
Params:
context – the context in which to set the value of the expression
rootObject – the root object against which to evaluate the expression
value – the new value
Throws:
EvaluationException – if there is a problem during evaluation/**
	 * Set this expression in the provided context to the value provided.
	 * The supplied root object overrides any specified in the context.
	 * @param context the context in which to set the value of the expression
	 * @param rootObject the root object against which to evaluate the expression
	 * @param value the new value
	 * @throws EvaluationException if there is a problem during evaluation
	 */
	void setValue(EvaluationContext context, @Nullable Object rootObject, @Nullable Object value) throws EvaluationException;

}