javax.el.Expression Maven / Gradle / Ivy
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package javax.el;
import java.io.Serializable;
/**
* Base class for the expression subclasses {@link ValueExpression} and
* {@link MethodExpression}, implementing characterstics common to both.
*
* All expressions must implement the equals() and
* hashCode() methods so that two expressions can be compared
* for equality. They are redefined abstract in this class to force their
* implementation in subclasses.
*
* All expressions must also be Serializable so that they
* can be saved and restored.
*
* Expressions are also designed to be immutable so
* that only one instance needs to be created for any given expression
* String / {@link FunctionMapper}. This allows a container to pre-create
* expressions and not have to re-parse them each time they are evaluated.
*
* @since JSP 2.1
*/
public abstract class Expression
implements Serializable {
// Debugging
/**
* Returns the original String used to create this Expression,
* unmodified.
*
* This is used for debugging purposes but also for the purposes
* of comparison (e.g. to ensure the expression in a configuration
* file has not changed).
*
* This method does not provide sufficient information to
* re-create an expression. Two different expressions can have exactly
* the same expression string but different function mappings.
* Serialization should be used to save and restore the state of an
* Expression.
*
* @return The original expression String.
*/
public abstract String getExpressionString();
// Comparison
/**
* Determines whether the specified object is equal to this
* Expression.
*
* The result is true if and only if the argument is
* not null, is an Expression object that
* is the of the same type (ValueExpression or
* MethodExpression), and has an identical parsed
* representation.
*
* Note that two expressions can be equal if their expression
* Strings are different. For example, ${fn1:foo()}
* and ${fn2:foo()} are equal if their corresponding
* FunctionMappers mapped fn1:foo and
* fn2:foo to the same method.
*
* @param obj the Object to test for equality.
* @return true if obj equals this
* Expression; false otherwise.
* @see java.util.Hashtable
* @see java.lang.Object#equals(java.lang.Object)
*/
public abstract boolean equals(Object obj);
/**
* Returns the hash code for this Expression.
*
* See the note in the {@link #equals} method on how two expressions
* can be equal if their expression Strings are different. Recall that
* if two objects are equal according to the equals(Object)
* method, then calling the hashCode method on each of the
* two objects must produce the same integer result. Implementations must
* take special note and implement hashCode correctly.
*
* @return The hash code for this Expression.
* @see #equals
* @see java.util.Hashtable
* @see java.lang.Object#hashCode()
*/
public abstract int hashCode();
/**
* Returns whether this expression was created from only literal text.
*
* This method must return true if and only if the
* expression string this expression was created from contained no
* unescaped EL delimeters (${...} or
* #{...}).
*
* @return true if this expression was created from only
* literal text; false otherwise.
*/
public abstract boolean isLiteralText();
}