Package net.sourceforge.pmd.lang.java.ast

Interface ASTExpression

All Superinterfaces:

ASTMemberValue, ASTSwitchArrowRHS, GenericNode<JavaNode>, JavaNode, JjtreeNode<JavaNode>, Node, Reportable, TextAvailableNode, TypeNode

All Known Subinterfaces:

ASTAssignableExpr, ASTAssignableExpr.ASTNamedReferenceExpr, ASTLiteral, ASTPrimaryExpression, FunctionalExpression, QualifiableExpression

All Known Implementing Classes:

ASTAmbiguousName, ASTArrayAccess, ASTArrayAllocation, ASTArrayInitializer, ASTAssignmentExpression, ASTBooleanLiteral, ASTCastExpression, ASTCharLiteral, ASTClassLiteral, ASTConditionalExpression, ASTConstructorCall, ASTFieldAccess, ASTInfixExpression, ASTLambdaExpression, ASTMethodCall, ASTMethodReference, ASTNullLiteral, ASTNumericLiteral, ASTPatternExpression, ASTStringLiteral, ASTSuperExpression, ASTSwitchExpression, ASTThisExpression, ASTTypeExpression, ASTUnaryExpression, ASTVariableAccess

public interface ASTExpression
extends JavaNode, TypeNode, ASTMemberValue, ASTSwitchArrowRHS

Represents an expression, in the most general sense. This corresponds to the Expression of the JLS.

From 7.0.0 on, this is an interface which all expression nodes implement.

Expressions are required to be constant in some parts of the grammar (in SwitchLabel, Annotation, DefaultValue). A constant expression is represented as a normal expression subtree, which does not feature any MethodReference, LambdaExpression or AssignmentExpression.

 (: In increasing precedence order :)
 Expression ::= AssignmentExpression
              | ConditionalExpression
              | LambdaExpression
              | InfixExpression
              | PrefixExpression | CastExpression
              | PostfixExpression
              | SwitchExpression
              | PrimaryExpression

 

Field Summary

Fields inherited from interface net.sourceforge.pmd.lang.ast.Node

COORDS_COMPARATOR

Method Summary

Modifier and Type	Method	Description
default @Nullable Object	getConstValue()	Returns the constant value of this node, if this is a constant expression.
default @NonNull ExprContext	getConversionContext()	Returns the type expected by the context.
int	getParenthesisDepth()	Returns the number of parenthesis levels around this expression.
default boolean	isCompileTimeConstant()	Returns true if this expression is a compile-time constant, and is inlined.
default boolean	isExpression()	Always returns true.
default boolean	isParenthesized()	Returns true if this expression has at least one level of parentheses.

Methods inherited from interface net.sourceforge.pmd.lang.ast.impl.GenericNode

ancestors, ancestorsOrSelf, asStream, children, descendants, descendantsOrSelf, getChild, getFirstChild, getLastChild, getNextSibling, getNthParent, getParent, getPreviousSibling

Methods inherited from interface net.sourceforge.pmd.lang.java.ast.JavaNode

getEnclosingType, getRoot, getSymbolTable, getTypeSystem, jjtAccept

Methods inherited from interface net.sourceforge.pmd.lang.ast.impl.javacc.JjtreeNode

getFirstToken, getLastToken, tokens

Methods inherited from interface net.sourceforge.pmd.lang.ast.Node

acceptVisitor, ancestors, children, compareLocation, descendants, findChildNodesWithXPath, findChildrenOfType, findDescendantsOfType, findDescendantsOfType, firstChild, getAstInfo, getBeginColumn, getBeginLine, getEndColumn, getEndLine, getFirstChildOfType, getFirstDescendantOfType, getFirstParentOfType, getImage, getIndexInParent, getLanguageVersion, getNumChildren, getParentsOfType, getReportLocation, getTextDocument, getUserMap, getXPathAttributesIterator, getXPathNodeName, hasDescendantOfType, hasImageEqualTo, isFindBoundary

Methods inherited from interface net.sourceforge.pmd.lang.ast.TextAvailableNode

getOriginalText, getText, getTextRegion

Methods inherited from interface net.sourceforge.pmd.lang.java.ast.TypeNode

getType, getTypeMirror, getTypeMirror

Method Detail

isExpression

default boolean isExpression()

Always returns true. This is to allow XPath queries to query like /*[@Expression=true()] to match any expression, but is useless in Java code.

getParenthesisDepth

int getParenthesisDepth()

Returns the number of parenthesis levels around this expression. If this method returns 0, then no parentheses are present.

E.g. the expression (a + b) is parsed as an AdditiveExpression whose parenthesisDepth is 1, and in ((a + b)) it's 2.

This is to avoid the parentheses interfering with analysis. Parentheses already influence parsing by breaking the natural precedence of operators. It would mostly hide false positives to make a ParenthesizedExpr node, because it would make semantically equivalent nodes have a very different representation.

On the other hand, when a rule explicitly cares about parentheses, then this attribute may be used to find out whether parentheses were mentioned, so no information is lost.

isParenthesized

default boolean isParenthesized()

Returns true if this expression has at least one level of parentheses. The specific depth can be fetched with getParenthesisDepth().

getConstValue

default @Nullable Object getConstValue()

Description copied from interface: ASTMemberValue

Returns the constant value of this node, if this is a constant expression. Otherwise, or if some references couldn't be resolved, returns null. Note that null is not a constant value, so this method's returning null is not a problem. Note that annotations are not given a constant value by this implementation.

Specified by:

getConstValue in interface ASTMemberValue

isCompileTimeConstant

default boolean isCompileTimeConstant()

Returns true if this expression is a compile-time constant, and is inlined.

getConversionContext

@Experimental
default @NonNull ExprContext getConversionContext()

Returns the type expected by the context. This type may determine an implicit conversion of this value to that type (eg a boxing conversion, widening numeric conversion, or widening reference conversion).

There are many different cases. For example, in arr['c'], TypeNode.getTypeMirror() would return char for the char literal, but the context type is int since it's used as an array index. Hence, a widening conversion occurs. Similarly, the context type of an expression in a return statement is the return type of the method, etc.

If the context is undefined, then the returned object will answer true to ExprContext.isMissing(). This is completely normal and needs to be accounted for by rules. For instance, it occurs if this expression is used as a statement.

Note that conversions are a language-level construct only. Converting from a type to another may not actually require any concrete operation at runtime. For instance, converting a char to an int is a noop at runtime, because chars are anyway treated as ints by the JVM (within stack frames). A boxing conversion will however in general translate to a call to e.g. Integer.valueOf(int).

Not all contexts allow all kinds of conversions. See ExprContext.