Class Expression
- java.lang.Object
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- jakarta.el.Expression
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- All Implemented Interfaces:
Serializable
- Direct Known Subclasses:
MethodExpression
,ValueExpression
public abstract class Expression extends Object implements Serializable
Base class for the expression subclassesValueExpression
andMethodExpression
, implementing characteristics common to both.All expressions must implement the
equals()
andhashCode()
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.Expression
s are also designed to be immutable so that only one instance needs to be created for any given expression String /FunctionMapper
. This allows a container to pre-create expressions and not have to re-parse them each time they are evaluated.- Since:
- Jakarta Server Pages 2.1
- See Also:
- Serialized Form
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Constructor Summary
Constructors Constructor Description Expression()
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Method Summary
All Methods Instance Methods Abstract Methods Modifier and Type Method Description abstract boolean
equals(Object obj)
Determines whether the specified object is equal to thisExpression
.abstract String
getExpressionString()
Returns the original String used to create thisExpression
, unmodified.abstract int
hashCode()
Returns the hash code for thisExpression
.abstract boolean
isLiteralText()
Returns whether this expression was created from only literal text.
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Method Detail
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getExpressionString
public abstract String getExpressionString()
Returns the original String used to create thisExpression
, 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
.- Returns:
- The original expression String.
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equals
public abstract boolean equals(Object obj)
Determines whether the specified object is equal to thisExpression
.The result is
true
if and only if the argument is notnull
, is anExpression
object that is the of the same type (ValueExpression
orMethodExpression
), 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 correspondingFunctionMapper
s mappedfn1:foo
andfn2:foo
to the same method.- Overrides:
equals
in classObject
- Parameters:
obj
- theObject
to test for equality.- Returns:
true
ifobj
equals thisExpression
;false
otherwise.- See Also:
Hashtable
,Object.equals(java.lang.Object)
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hashCode
public abstract int hashCode()
Returns the hash code for thisExpression
.See the note in the
equals(java.lang.Object)
method on how two expressions can be equal if their expression Strings are different. Recall that if two objects are equal according to theequals(Object)
method, then calling thehashCode
method on each of the two objects must produce the same integer result. Implementations must take special note and implementhashCode
correctly.- Overrides:
hashCode
in classObject
- Returns:
- The hash code for this
Expression
. - See Also:
equals(java.lang.Object)
,Hashtable
,Object.hashCode()
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isLiteralText
public abstract boolean isLiteralText()
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 Jakarta Expression Language delimeters (${...}
or#{...}
).- Returns:
true
if this expression was created from only literal text;false
otherwise.
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