////////////////////////////////////////////////////////////////////////////////
// checkstyle: Checks Java source code for adherence to a set of rules.
// Copyright (C) 2001-2017 the original author or authors.
//
// This library is free software; you can redistribute it and/or
// modify it under the terms of the GNU Lesser General Public
// License as published by the Free Software Foundation; either
// version 2.1 of the License, or (at your option) any later version.
//
// This library is distributed in the hope that it will be useful,
// but WITHOUT ANY WARRANTY; without even the implied warranty of
// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
// Lesser General Public License for more details.
//
// You should have received a copy of the GNU Lesser General Public
// License along with this library; if not, write to the Free Software
// Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA
////////////////////////////////////////////////////////////////////////////////
package com.puppycrawl.tools.checkstyle.checks.coding;
import java.util.Collections;
import java.util.HashSet;
import java.util.Set;
import com.puppycrawl.tools.checkstyle.api.AbstractCheck;
import com.puppycrawl.tools.checkstyle.api.DetailAST;
import com.puppycrawl.tools.checkstyle.api.TokenTypes;
/**
* Checks that any combination of String literals
* is on the left side of an equals() comparison.
* Also checks for String literals assigned to some field
* (such as <code>someString.equals(anotherString = "text")</code>).
*
* <p>Rationale: Calling the equals() method on String literals
* will avoid a potential NullPointerException. Also, it is
* pretty common to see null check right before equals comparisons
* which is not necessary in the below example.
*
* <p>For example:
*
* <pre>
* {@code
* String nullString = null;
* nullString.equals("My_Sweet_String");
* }
* </pre>
* should be refactored to
*
* <pre>
* {@code
* String nullString = null;
* "My_Sweet_String".equals(nullString);
* }
* </pre>
*
* @author Travis Schneeberger
* @author Vladislav Lisetskiy
*/
public class EqualsAvoidNullCheck extends AbstractCheck {
/**
* A key is pointing to the warning message text in "messages.properties"
* file.
*/
public static final String MSG_EQUALS_AVOID_NULL = "equals.avoid.null";
/**
* A key is pointing to the warning message text in "messages.properties"
* file.
*/
public static final String MSG_EQUALS_IGNORE_CASE_AVOID_NULL = "equalsIgnoreCase.avoid.null";
/** Method name for comparison. */
private static final String EQUALS = "equals";
/** Type name for comparison. */
private static final String STRING = "String";
/** Whether to process equalsIgnoreCase() invocations. */
private boolean ignoreEqualsIgnoreCase;
/** Stack of sets of field names, one for each class of a set of nested classes. */
private FieldFrame currentFrame;
@Override
public int[] getDefaultTokens() {
return getAcceptableTokens();
}
@Override
public int[] getAcceptableTokens() {
return new int[] {
TokenTypes.METHOD_CALL,
TokenTypes.CLASS_DEF,
TokenTypes.METHOD_DEF,
TokenTypes.LITERAL_IF,
TokenTypes.LITERAL_FOR,
TokenTypes.LITERAL_WHILE,
TokenTypes.LITERAL_DO,
TokenTypes.LITERAL_CATCH,
TokenTypes.LITERAL_TRY,
TokenTypes.VARIABLE_DEF,
TokenTypes.PARAMETER_DEF,
TokenTypes.CTOR_DEF,
TokenTypes.SLIST,
TokenTypes.ENUM_DEF,
TokenTypes.ENUM_CONSTANT_DEF,
TokenTypes.LITERAL_NEW,
};
}
@Override
public int[] getRequiredTokens() {
return getAcceptableTokens();
}
/**
* Whether to ignore checking {@code String.equalsIgnoreCase(String)}.
* @param newValue whether to ignore checking
* {@code String.equalsIgnoreCase(String)}.
*/
public void setIgnoreEqualsIgnoreCase(boolean newValue) {
ignoreEqualsIgnoreCase = newValue;
}
@Override
public void beginTree(DetailAST rootAST) {
currentFrame = new FieldFrame(null);
}
@Override
public void visitToken(final DetailAST ast) {
switch (ast.getType()) {
case TokenTypes.VARIABLE_DEF:
case TokenTypes.PARAMETER_DEF:
currentFrame.addField(ast);
break;
case TokenTypes.METHOD_CALL:
processMethodCall(ast);
break;
case TokenTypes.SLIST:
processSlist(ast);
break;
case TokenTypes.LITERAL_NEW:
processLiteralNew(ast);
break;
default:
processFrame(ast);
}
}
@Override
public void leaveToken(DetailAST ast) {
final int astType = ast.getType();
if (astType != TokenTypes.VARIABLE_DEF
&& astType != TokenTypes.PARAMETER_DEF
&& astType != TokenTypes.METHOD_CALL
&& astType != TokenTypes.SLIST
&& astType != TokenTypes.LITERAL_NEW
|| astType == TokenTypes.LITERAL_NEW
&& ast.branchContains(TokenTypes.LCURLY)) {
currentFrame = currentFrame.getParent();
}
else if (astType == TokenTypes.SLIST) {
leaveSlist(ast);
}
}
@Override
public void finishTree(DetailAST ast) {
traverseFieldFrameTree(currentFrame);
}
/**
* Determine whether SLIST begins static or non-static block and add it as
* a frame in this case.
* @param ast SLIST ast.
*/
private void processSlist(DetailAST ast) {
final int parentType = ast.getParent().getType();
if (parentType == TokenTypes.SLIST
|| parentType == TokenTypes.STATIC_INIT
|| parentType == TokenTypes.INSTANCE_INIT) {
final FieldFrame frame = new FieldFrame(currentFrame);
currentFrame.addChild(frame);
currentFrame = frame;
}
}
/**
* Determine whether SLIST begins static or non-static block and
* @param ast SLIST ast.
*/
private void leaveSlist(DetailAST ast) {
final int parentType = ast.getParent().getType();
if (parentType == TokenTypes.SLIST
|| parentType == TokenTypes.STATIC_INIT
|| parentType == TokenTypes.INSTANCE_INIT) {
currentFrame = currentFrame.getParent();
}
}
/**
* Process CLASS_DEF, METHOD_DEF, LITERAL_IF, LITERAL_FOR, LITERAL_WHILE, LITERAL_DO,
* LITERAL_CATCH, LITERAL_TRY, CTOR_DEF, ENUM_DEF, ENUM_CONSTANT_DEF.
* @param ast processed ast.
*/
private void processFrame(DetailAST ast) {
final FieldFrame frame = new FieldFrame(currentFrame);
final int astType = ast.getType();
if (astType == TokenTypes.CLASS_DEF
|| astType == TokenTypes.ENUM_DEF
|| astType == TokenTypes.ENUM_CONSTANT_DEF) {
frame.setClassOrEnumOrEnumConstDef(true);
frame.setFrameName(ast.findFirstToken(TokenTypes.IDENT).getText());
}
currentFrame.addChild(frame);
currentFrame = frame;
}
/**
* Add the method call to the current frame if it should be processed.
* @param methodCall METHOD_CALL ast.
*/
private void processMethodCall(DetailAST methodCall) {
final DetailAST dot = methodCall.getFirstChild();
if (dot.getType() == TokenTypes.DOT) {
final String methodName = dot.getLastChild().getText();
if (EQUALS.equals(methodName)
|| !ignoreEqualsIgnoreCase && "equalsIgnoreCase".equals(methodName)) {
currentFrame.addMethodCall(methodCall);
}
}
}
/**
* Determine whether LITERAL_NEW is an anonymous class definition and add it as
* a frame in this case.
* @param ast LITERAL_NEW ast.
*/
private void processLiteralNew(DetailAST ast) {
if (ast.branchContains(TokenTypes.LCURLY)) {
final FieldFrame frame = new FieldFrame(currentFrame);
currentFrame.addChild(frame);
currentFrame = frame;
}
}
/**
* Traverse the tree of the field frames to check all equals method calls.
* @param frame to check method calls in.
*/
private void traverseFieldFrameTree(FieldFrame frame) {
for (FieldFrame child: frame.getChildren()) {
if (!child.getChildren().isEmpty()) {
traverseFieldFrameTree(child);
}
currentFrame = child;
child.getMethodCalls().forEach(this::checkMethodCall);
}
}
/**
* Check whether the method call should be violated.
* @param methodCall method call to check.
*/
private void checkMethodCall(DetailAST methodCall) {
DetailAST objCalledOn = methodCall.getFirstChild().getFirstChild();
if (objCalledOn.getType() == TokenTypes.DOT) {
objCalledOn = objCalledOn.getLastChild();
}
final DetailAST expr = methodCall.findFirstToken(TokenTypes.ELIST).getFirstChild();
if (isObjectValid(objCalledOn)
&& containsOneArgument(methodCall)
&& containsAllSafeTokens(expr)
&& isCalledOnStringFieldOrVariable(objCalledOn)) {
final String methodName = methodCall.getFirstChild().getLastChild().getText();
if (EQUALS.equals(methodName)) {
log(methodCall.getLineNo(), methodCall.getColumnNo(),
MSG_EQUALS_AVOID_NULL);
}
else {
log(methodCall.getLineNo(), methodCall.getColumnNo(),
MSG_EQUALS_IGNORE_CASE_AVOID_NULL);
}
}
}
/**
* Check whether the object equals method is called on is not a String literal
* and not too complex.
* @param objCalledOn the object equals method is called on ast.
* @return true if the object is valid.
*/
private static boolean isObjectValid(DetailAST objCalledOn) {
boolean result = true;
final DetailAST previousSibling = objCalledOn.getPreviousSibling();
if (previousSibling != null
&& previousSibling.getType() == TokenTypes.DOT) {
result = false;
}
if (isStringLiteral(objCalledOn)) {
result = false;
}
return result;
}
/**
* Checks for calling equals on String literal and
* anon object which cannot be null.
* @param objCalledOn object AST
* @return if it is string literal
*/
private static boolean isStringLiteral(DetailAST objCalledOn) {
return objCalledOn.getType() == TokenTypes.STRING_LITERAL
|| objCalledOn.getType() == TokenTypes.LITERAL_NEW;
}
/**
* Verify that method call has one argument.
*
* @param methodCall METHOD_CALL DetailAST
* @return true if method call has one argument.
*/
private static boolean containsOneArgument(DetailAST methodCall) {
final DetailAST elist = methodCall.findFirstToken(TokenTypes.ELIST);
return elist.getChildCount() == 1;
}
/**
* Looks for all "safe" Token combinations in the argument
* expression branch.
* @param expr the argument expression
* @return - true if any child matches the set of tokens, false if not
*/
private static boolean containsAllSafeTokens(final DetailAST expr) {
DetailAST arg = expr.getFirstChild();
arg = skipVariableAssign(arg);
boolean argIsNotNull = false;
if (arg.getType() == TokenTypes.PLUS) {
DetailAST child = arg.getFirstChild();
while (child != null
&& !argIsNotNull) {
argIsNotNull = child.getType() == TokenTypes.STRING_LITERAL
|| child.getType() == TokenTypes.IDENT;
child = child.getNextSibling();
}
}
return argIsNotNull
|| !arg.branchContains(TokenTypes.IDENT)
&& !arg.branchContains(TokenTypes.LITERAL_NULL);
}
/**
* Skips over an inner assign portion of an argument expression.
* @param currentAST current token in the argument expression
* @return the next relevant token
*/
private static DetailAST skipVariableAssign(final DetailAST currentAST) {
if (currentAST.getType() == TokenTypes.ASSIGN
&& currentAST.getFirstChild().getType() == TokenTypes.IDENT) {
return currentAST.getFirstChild().getNextSibling();
}
return currentAST;
}
/**
* Determine, whether equals method is called on a field of String type.
* @param objCalledOn object ast.
* @return true if the object is of String type.
*/
private boolean isCalledOnStringFieldOrVariable(DetailAST objCalledOn) {
final boolean result;
final DetailAST previousSiblingAst = objCalledOn.getPreviousSibling();
if (previousSiblingAst == null) {
result = isStringFieldOrVariable(objCalledOn);
}
else {
if (previousSiblingAst.getType() == TokenTypes.LITERAL_THIS) {
result = isStringFieldOrVariableFromThisInstance(objCalledOn);
}
else {
final String className = previousSiblingAst.getText();
result = isStringFieldOrVariableFromClass(objCalledOn, className);
}
}
return result;
}
/**
* Whether the field or the variable is of String type.
* @param objCalledOn the field or the variable to check.
* @return true if the field or the variable is of String type.
*/
private boolean isStringFieldOrVariable(DetailAST objCalledOn) {
boolean result = false;
final String name = objCalledOn.getText();
FieldFrame frame = currentFrame;
while (frame != null) {
final DetailAST field = frame.findField(name);
if (field != null
&& (frame.isClassOrEnumOrEnumConstDef()
|| checkLineNo(field, objCalledOn))) {
result = STRING.equals(getFieldType(field));
break;
}
frame = frame.getParent();
}
return result;
}
/**
* Whether the field or the variable from THIS instance is of String type.
* @param objCalledOn the field or the variable from THIS instance to check.
* @return true if the field or the variable from THIS instance is of String type.
*/
private boolean isStringFieldOrVariableFromThisInstance(DetailAST objCalledOn) {
boolean result = false;
final String name = objCalledOn.getText();
final DetailAST field = getObjectFrame(currentFrame).findField(name);
if (field != null) {
result = STRING.equals(getFieldType(field));
}
return result;
}
/**
* Whether the field or the variable from the specified class is of String type.
* @param objCalledOn the field or the variable from the specified class to check.
* @param className the name of the class to check in.
* @return true if the field or the variable from the specified class is of String type.
*/
private boolean isStringFieldOrVariableFromClass(DetailAST objCalledOn,
final String className) {
boolean result = false;
final String name = objCalledOn.getText();
FieldFrame frame = getObjectFrame(currentFrame);
while (frame != null) {
if (className.equals(frame.getFrameName())) {
final DetailAST field = frame.findField(name);
if (field != null) {
result = STRING.equals(getFieldType(field));
}
break;
}
frame = getObjectFrame(frame.getParent());
}
return result;
}
/**
* Get the nearest parent frame which is CLASS_DEF, ENUM_DEF or ENUM_CONST_DEF.
* @param frame to start the search from.
* @return the nearest parent frame which is CLASS_DEF, ENUM_DEF or ENUM_CONST_DEF.
*/
private static FieldFrame getObjectFrame(FieldFrame frame) {
FieldFrame objectFrame = frame;
while (objectFrame != null && !objectFrame.isClassOrEnumOrEnumConstDef()) {
objectFrame = objectFrame.getParent();
}
return objectFrame;
}
/**
* Check whether the field is declared before the method call in case of
* methods and initialization blocks.
* @param field field to check.
* @param objCalledOn object equals method called on.
* @return true if the field is declared before the method call.
*/
private static boolean checkLineNo(DetailAST field, DetailAST objCalledOn) {
boolean result = false;
if (field.getLineNo() < objCalledOn.getLineNo()
|| field.getLineNo() == objCalledOn.getLineNo()
&& field.getColumnNo() < objCalledOn.getColumnNo()) {
result = true;
}
return result;
}
/**
* Get field type.
* @param field to get the type from.
* @return type of the field.
*/
private static String getFieldType(DetailAST field) {
String fieldType = null;
final DetailAST identAst = field.findFirstToken(TokenTypes.TYPE)
.findFirstToken(TokenTypes.IDENT);
if (identAst != null) {
fieldType = identAst.getText();
}
return fieldType;
}
/**
* Holds the names of fields of a type.
*/
private static class FieldFrame {
/** Parent frame. */
private final FieldFrame parent;
/** Set of frame's children. */
private final Set<FieldFrame> children = new HashSet<>();
/** Set of fields. */
private final Set<DetailAST> fields = new HashSet<>();
/** Set of equals calls. */
private final Set<DetailAST> methodCalls = new HashSet<>();
/** Name of the class, enum or enum constant declaration. */
private String frameName;
/** Whether the frame is CLASS_DEF, ENUM_DEF or ENUM_CONST_DEF. */
private boolean classOrEnumOrEnumConstDef;
/**
* Creates new frame.
* @param parent parent frame.
*/
FieldFrame(FieldFrame parent) {
this.parent = parent;
}
/**
* Set the frame name.
* @param frameName value to set.
*/
public void setFrameName(String frameName) {
this.frameName = frameName;
}
/**
* Getter for the frame name.
* @return frame name.
*/
public String getFrameName() {
return frameName;
}
/**
* Getter for the parent frame.
* @return parent frame.
*/
public FieldFrame getParent() {
return parent;
}
/**
* Getter for frame's children.
* @return children of this frame.
*/
public Set<FieldFrame> getChildren() {
return Collections.unmodifiableSet(children);
}
/**
* Add child frame to this frame.
* @param child frame to add.
*/
public void addChild(FieldFrame child) {
children.add(child);
}
/**
* Add field to this FieldFrame.
* @param field the ast of the field.
*/
public void addField(DetailAST field) {
fields.add(field);
}
/**
* Sets isClassOrEnum.
* @param value value to set.
*/
public void setClassOrEnumOrEnumConstDef(boolean value) {
classOrEnumOrEnumConstDef = value;
}
/**
* Getter for classOrEnumOrEnumConstDef.
* @return classOrEnumOrEnumConstDef.
*/
public boolean isClassOrEnumOrEnumConstDef() {
return classOrEnumOrEnumConstDef;
}
/**
* Add method call to this frame.
* @param methodCall METHOD_CALL ast.
*/
public void addMethodCall(DetailAST methodCall) {
methodCalls.add(methodCall);
}
/**
* Determines whether this FieldFrame contains the field.
* @param name name of the field to check.
* @return true if this FieldFrame contains instance field field.
*/
public DetailAST findField(String name) {
for (DetailAST field: fields) {
if (getFieldName(field).equals(name)) {
return field;
}
}
return null;
}
/**
* Getter for frame's method calls.
* @return method calls of this frame.
*/
public Set<DetailAST> getMethodCalls() {
return Collections.unmodifiableSet(methodCalls);
}
/**
* Get the name of the field.
* @param field to get the name from.
* @return name of the field.
*/
private static String getFieldName(DetailAST field) {
return field.findFirstToken(TokenTypes.IDENT).getText();
}
}
}