001//////////////////////////////////////////////////////////////////////////////// 002// checkstyle: Checks Java source code for adherence to a set of rules. 003// Copyright (C) 2001-2016 the original author or authors. 004// 005// This library is free software; you can redistribute it and/or 006// modify it under the terms of the GNU Lesser General Public 007// License as published by the Free Software Foundation; either 008// version 2.1 of the License, or (at your option) any later version. 009// 010// This library is distributed in the hope that it will be useful, 011// but WITHOUT ANY WARRANTY; without even the implied warranty of 012// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU 013// Lesser General Public License for more details. 014// 015// You should have received a copy of the GNU Lesser General Public 016// License along with this library; if not, write to the Free Software 017// Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA 018//////////////////////////////////////////////////////////////////////////////// 019 020package com.puppycrawl.tools.checkstyle.checks.coding; 021 022import java.util.Collections; 023import java.util.Set; 024 025import com.google.common.collect.Sets; 026import com.puppycrawl.tools.checkstyle.api.AbstractCheck; 027import com.puppycrawl.tools.checkstyle.api.DetailAST; 028import com.puppycrawl.tools.checkstyle.api.TokenTypes; 029 030/** 031 * Checks that any combination of String literals 032 * is on the left side of an equals() comparison. 033 * Also checks for String literals assigned to some field 034 * (such as <code>someString.equals(anotherString = "text")</code>). 035 * 036 * <p>Rationale: Calling the equals() method on String literals 037 * will avoid a potential NullPointerException. Also, it is 038 * pretty common to see null check right before equals comparisons 039 * which is not necessary in the below example. 040 * 041 * <p>For example: 042 * 043 * <pre> 044 * {@code 045 * String nullString = null; 046 * nullString.equals("My_Sweet_String"); 047 * } 048 * </pre> 049 * should be refactored to 050 * 051 * <pre> 052 * {@code 053 * String nullString = null; 054 * "My_Sweet_String".equals(nullString); 055 * } 056 * </pre> 057 * 058 * @author Travis Schneeberger 059 * @author Vladislav Lisetskiy 060 */ 061public class EqualsAvoidNullCheck extends AbstractCheck { 062 063 /** 064 * A key is pointing to the warning message text in "messages.properties" 065 * file. 066 */ 067 public static final String MSG_EQUALS_AVOID_NULL = "equals.avoid.null"; 068 069 /** 070 * A key is pointing to the warning message text in "messages.properties" 071 * file. 072 */ 073 public static final String MSG_EQUALS_IGNORE_CASE_AVOID_NULL = "equalsIgnoreCase.avoid.null"; 074 075 /** Method name for comparison. */ 076 private static final String EQUALS = "equals"; 077 078 /** Type name for comparison. */ 079 private static final String STRING = "String"; 080 081 /** Whether to process equalsIgnoreCase() invocations. */ 082 private boolean ignoreEqualsIgnoreCase; 083 084 /** Stack of sets of field names, one for each class of a set of nested classes. */ 085 private FieldFrame currentFrame; 086 087 @Override 088 public int[] getDefaultTokens() { 089 return getAcceptableTokens(); 090 } 091 092 @Override 093 public int[] getAcceptableTokens() { 094 return new int[] { 095 TokenTypes.METHOD_CALL, 096 TokenTypes.CLASS_DEF, 097 TokenTypes.METHOD_DEF, 098 TokenTypes.LITERAL_IF, 099 TokenTypes.LITERAL_FOR, 100 TokenTypes.LITERAL_WHILE, 101 TokenTypes.LITERAL_DO, 102 TokenTypes.LITERAL_CATCH, 103 TokenTypes.LITERAL_TRY, 104 TokenTypes.VARIABLE_DEF, 105 TokenTypes.PARAMETER_DEF, 106 TokenTypes.CTOR_DEF, 107 TokenTypes.SLIST, 108 TokenTypes.ENUM_DEF, 109 TokenTypes.ENUM_CONSTANT_DEF, 110 TokenTypes.LITERAL_NEW, 111 }; 112 } 113 114 @Override 115 public int[] getRequiredTokens() { 116 return getAcceptableTokens(); 117 } 118 119 /** 120 * Whether to ignore checking {@code String.equalsIgnoreCase(String)}. 121 * @param newValue whether to ignore checking 122 * {@code String.equalsIgnoreCase(String)}. 123 */ 124 public void setIgnoreEqualsIgnoreCase(boolean newValue) { 125 ignoreEqualsIgnoreCase = newValue; 126 } 127 128 @Override 129 public void beginTree(DetailAST rootAST) { 130 currentFrame = new FieldFrame(null); 131 } 132 133 @Override 134 public void visitToken(final DetailAST ast) { 135 switch (ast.getType()) { 136 case TokenTypes.VARIABLE_DEF: 137 case TokenTypes.PARAMETER_DEF: 138 currentFrame.addField(ast); 139 break; 140 case TokenTypes.METHOD_CALL: 141 processMethodCall(ast); 142 break; 143 case TokenTypes.SLIST: 144 processSlist(ast); 145 break; 146 case TokenTypes.LITERAL_NEW: 147 processLiteralNew(ast); 148 break; 149 default: 150 processFrame(ast); 151 } 152 } 153 154 @Override 155 public void leaveToken(DetailAST ast) { 156 final int astType = ast.getType(); 157 if (astType != TokenTypes.VARIABLE_DEF 158 && astType != TokenTypes.PARAMETER_DEF 159 && astType != TokenTypes.METHOD_CALL 160 && astType != TokenTypes.SLIST 161 && astType != TokenTypes.LITERAL_NEW 162 || astType == TokenTypes.LITERAL_NEW 163 && ast.branchContains(TokenTypes.LCURLY)) { 164 currentFrame = currentFrame.getParent(); 165 } 166 else if (astType == TokenTypes.SLIST) { 167 leaveSlist(ast); 168 } 169 } 170 171 @Override 172 public void finishTree(DetailAST ast) { 173 traverseFieldFrameTree(currentFrame); 174 } 175 176 /** 177 * Determine whether SLIST begins static or non-static block and add it as 178 * a frame in this case. 179 * @param ast SLIST ast. 180 */ 181 private void processSlist(DetailAST ast) { 182 final int parentType = ast.getParent().getType(); 183 if (parentType == TokenTypes.SLIST 184 || parentType == TokenTypes.STATIC_INIT 185 || parentType == TokenTypes.INSTANCE_INIT) { 186 final FieldFrame frame = new FieldFrame(currentFrame); 187 currentFrame.addChild(frame); 188 currentFrame = frame; 189 } 190 } 191 192 /** 193 * Determine whether SLIST begins static or non-static block and 194 * @param ast SLIST ast. 195 */ 196 private void leaveSlist(DetailAST ast) { 197 final int parentType = ast.getParent().getType(); 198 if (parentType == TokenTypes.SLIST 199 || parentType == TokenTypes.STATIC_INIT 200 || parentType == TokenTypes.INSTANCE_INIT) { 201 currentFrame = currentFrame.getParent(); 202 } 203 } 204 205 /** 206 * Process CLASS_DEF, METHOD_DEF, LITERAL_IF, LITERAL_FOR, LITERAL_WHILE, LITERAL_DO, 207 * LITERAL_CATCH, LITERAL_TRY, CTOR_DEF, ENUM_DEF, ENUM_CONSTANT_DEF. 208 * @param ast processed ast. 209 */ 210 private void processFrame(DetailAST ast) { 211 final FieldFrame frame = new FieldFrame(currentFrame); 212 final int astType = ast.getType(); 213 if (astType == TokenTypes.CLASS_DEF 214 || astType == TokenTypes.ENUM_DEF 215 || astType == TokenTypes.ENUM_CONSTANT_DEF) { 216 frame.setClassOrEnumOrEnumConstDef(true); 217 frame.setFrameName(ast.findFirstToken(TokenTypes.IDENT).getText()); 218 } 219 currentFrame.addChild(frame); 220 currentFrame = frame; 221 } 222 223 /** 224 * Add the method call to the current frame if it should be processed. 225 * @param methodCall METHOD_CALL ast. 226 */ 227 private void processMethodCall(DetailAST methodCall) { 228 final DetailAST dot = methodCall.getFirstChild(); 229 if (dot.getType() == TokenTypes.DOT) { 230 final String methodName = dot.getLastChild().getText(); 231 if (EQUALS.equals(methodName) 232 || !ignoreEqualsIgnoreCase && "equalsIgnoreCase".equals(methodName)) { 233 currentFrame.addMethodCall(methodCall); 234 } 235 } 236 } 237 238 /** 239 * Determine whether LITERAL_NEW is an anonymous class definition and add it as 240 * a frame in this case. 241 * @param ast LITERAL_NEW ast. 242 */ 243 private void processLiteralNew(DetailAST ast) { 244 if (ast.branchContains(TokenTypes.LCURLY)) { 245 final FieldFrame frame = new FieldFrame(currentFrame); 246 currentFrame.addChild(frame); 247 currentFrame = frame; 248 } 249 } 250 251 /** 252 * Traverse the tree of the field frames to check all equals method calls. 253 * @param frame to check method calls in. 254 */ 255 private void traverseFieldFrameTree(FieldFrame frame) { 256 for (FieldFrame child: frame.getChildren()) { 257 if (!child.getChildren().isEmpty()) { 258 traverseFieldFrameTree(child); 259 } 260 currentFrame = child; 261 for (DetailAST methodCall: child.getMethodCalls()) { 262 checkMethodCall(methodCall); 263 } 264 } 265 } 266 267 /** 268 * Check whether the method call should be violated. 269 * @param methodCall method call to check. 270 */ 271 private void checkMethodCall(DetailAST methodCall) { 272 DetailAST objCalledOn = methodCall.getFirstChild().getFirstChild(); 273 if (objCalledOn.getType() == TokenTypes.DOT) { 274 objCalledOn = objCalledOn.getLastChild(); 275 } 276 final DetailAST expr = methodCall.findFirstToken(TokenTypes.ELIST).getFirstChild(); 277 if (isObjectValid(objCalledOn) 278 && containsOneArgument(methodCall) 279 && containsAllSafeTokens(expr) 280 && isCalledOnStringFieldOrVariable(objCalledOn)) { 281 final String methodName = methodCall.getFirstChild().getLastChild().getText(); 282 if (EQUALS.equals(methodName)) { 283 log(methodCall.getLineNo(), methodCall.getColumnNo(), 284 MSG_EQUALS_AVOID_NULL); 285 } 286 else { 287 log(methodCall.getLineNo(), methodCall.getColumnNo(), 288 MSG_EQUALS_IGNORE_CASE_AVOID_NULL); 289 } 290 } 291 } 292 293 /** 294 * Check whether the object equals method is called on is not a String literal 295 * and not too complex. 296 * @param objCalledOn the object equals method is called on ast. 297 * @return true if the object is valid. 298 */ 299 private static boolean isObjectValid(DetailAST objCalledOn) { 300 boolean result = true; 301 final DetailAST previousSibling = objCalledOn.getPreviousSibling(); 302 if (previousSibling != null 303 && previousSibling.getType() == TokenTypes.DOT) { 304 result = false; 305 } 306 if (isStringLiteral(objCalledOn)) { 307 result = false; 308 } 309 return result; 310 } 311 312 /** 313 * Checks for calling equals on String literal and 314 * anon object which cannot be null. 315 * @param objCalledOn object AST 316 * @return if it is string literal 317 */ 318 private static boolean isStringLiteral(DetailAST objCalledOn) { 319 return objCalledOn.getType() == TokenTypes.STRING_LITERAL 320 || objCalledOn.getType() == TokenTypes.LITERAL_NEW; 321 } 322 323 /** 324 * Verify that method call has one argument. 325 * 326 * @param methodCall METHOD_CALL DetailAST 327 * @return true if method call has one argument. 328 */ 329 private static boolean containsOneArgument(DetailAST methodCall) { 330 final DetailAST elist = methodCall.findFirstToken(TokenTypes.ELIST); 331 return elist.getChildCount() == 1; 332 } 333 334 /** 335 * Looks for all "safe" Token combinations in the argument 336 * expression branch. 337 * @param expr the argument expression 338 * @return - true if any child matches the set of tokens, false if not 339 */ 340 private boolean containsAllSafeTokens(final DetailAST expr) { 341 DetailAST arg = expr.getFirstChild(); 342 arg = skipVariableAssign(arg); 343 344 boolean argIsNotNull = false; 345 if (arg.getType() == TokenTypes.PLUS) { 346 DetailAST child = arg.getFirstChild(); 347 while (child != null 348 && !argIsNotNull) { 349 argIsNotNull = child.getType() == TokenTypes.STRING_LITERAL 350 || child.getType() == TokenTypes.IDENT; 351 child = child.getNextSibling(); 352 } 353 } 354 355 return argIsNotNull 356 || !arg.branchContains(TokenTypes.IDENT) 357 && !arg.branchContains(TokenTypes.LITERAL_NULL); 358 } 359 360 /** 361 * Skips over an inner assign portion of an argument expression. 362 * @param currentAST current token in the argument expression 363 * @return the next relevant token 364 */ 365 private static DetailAST skipVariableAssign(final DetailAST currentAST) { 366 if (currentAST.getType() == TokenTypes.ASSIGN 367 && currentAST.getFirstChild().getType() == TokenTypes.IDENT) { 368 return currentAST.getFirstChild().getNextSibling(); 369 } 370 return currentAST; 371 } 372 373 /** 374 * Determine, whether equals method is called on a field of String type. 375 * @param objCalledOn object ast. 376 * @return true if the object is of String type. 377 */ 378 private boolean isCalledOnStringFieldOrVariable(DetailAST objCalledOn) { 379 final boolean result; 380 final DetailAST previousSiblingAst = objCalledOn.getPreviousSibling(); 381 if (previousSiblingAst == null) { 382 result = isStringFieldOrVariable(objCalledOn); 383 } 384 else { 385 if (previousSiblingAst.getType() == TokenTypes.LITERAL_THIS) { 386 result = isStringFieldOrVariableFromThisInstance(objCalledOn); 387 } 388 else { 389 final String className = previousSiblingAst.getText(); 390 result = isStringFieldOrVariableFromClass(objCalledOn, className); 391 } 392 } 393 return result; 394 } 395 396 /** 397 * Whether the field or the variable is of String type. 398 * @param objCalledOn the field or the variable to check. 399 * @return true if the field or the variable is of String type. 400 */ 401 private boolean isStringFieldOrVariable(DetailAST objCalledOn) { 402 boolean result = false; 403 final String name = objCalledOn.getText(); 404 FieldFrame frame = currentFrame; 405 while (frame != null) { 406 final DetailAST field = frame.findField(name); 407 if (field != null 408 && (frame.isClassOrEnumOrEnumConstDef() 409 || checkLineNo(field, objCalledOn))) { 410 result = STRING.equals(getFieldType(field)); 411 break; 412 } 413 frame = frame.getParent(); 414 } 415 return result; 416 } 417 418 /** 419 * Whether the field or the variable from THIS instance is of String type. 420 * @param objCalledOn the field or the variable from THIS instance to check. 421 * @return true if the field or the variable from THIS instance is of String type. 422 */ 423 private boolean isStringFieldOrVariableFromThisInstance(DetailAST objCalledOn) { 424 boolean result = false; 425 final String name = objCalledOn.getText(); 426 final DetailAST field = getObjectFrame(currentFrame).findField(name); 427 if (field != null) { 428 result = STRING.equals(getFieldType(field)); 429 } 430 return result; 431 } 432 433 /** 434 * Whether the field or the variable from the specified class is of String type. 435 * @param objCalledOn the field or the variable from the specified class to check. 436 * @param className the name of the class to check in. 437 * @return true if the field or the variable from the specified class is of String type. 438 */ 439 private boolean isStringFieldOrVariableFromClass(DetailAST objCalledOn, 440 final String className) { 441 boolean result = false; 442 final String name = objCalledOn.getText(); 443 FieldFrame frame = getObjectFrame(currentFrame); 444 while (frame != null) { 445 if (className.equals(frame.getFrameName())) { 446 final DetailAST field = frame.findField(name); 447 if (field != null) { 448 result = STRING.equals(getFieldType(field)); 449 } 450 break; 451 } 452 frame = getObjectFrame(frame.getParent()); 453 } 454 return result; 455 } 456 457 /** 458 * Get the nearest parent frame which is CLASS_DEF, ENUM_DEF or ENUM_CONST_DEF. 459 * @param frame to start the search from. 460 * @return the nearest parent frame which is CLASS_DEF, ENUM_DEF or ENUM_CONST_DEF. 461 */ 462 private static FieldFrame getObjectFrame(FieldFrame frame) { 463 FieldFrame objectFrame = frame; 464 while (objectFrame != null && !objectFrame.isClassOrEnumOrEnumConstDef()) { 465 objectFrame = objectFrame.getParent(); 466 } 467 return objectFrame; 468 } 469 470 /** 471 * Check whether the field is declared before the method call in case of 472 * methods and initialization blocks. 473 * @param field field to check. 474 * @param objCalledOn object equals method called on. 475 * @return true if the field is declared before the method call. 476 */ 477 private static boolean checkLineNo(DetailAST field, DetailAST objCalledOn) { 478 boolean result = false; 479 if (field.getLineNo() < objCalledOn.getLineNo() 480 || field.getLineNo() == objCalledOn.getLineNo() 481 && field.getColumnNo() < objCalledOn.getColumnNo()) { 482 result = true; 483 } 484 return result; 485 } 486 487 /** 488 * Get field type. 489 * @param field to get the type from. 490 * @return type of the field. 491 */ 492 private static String getFieldType(DetailAST field) { 493 String fieldType = null; 494 final DetailAST identAst = field.findFirstToken(TokenTypes.TYPE) 495 .findFirstToken(TokenTypes.IDENT); 496 if (identAst != null) { 497 fieldType = identAst.getText(); 498 } 499 return fieldType; 500 } 501 502 /** 503 * Holds the names of fields of a type. 504 */ 505 private static class FieldFrame { 506 /** Parent frame. */ 507 private final FieldFrame parent; 508 509 /** Set of frame's children. */ 510 private final Set<FieldFrame> children = Sets.newHashSet(); 511 512 /** Set of fields. */ 513 private final Set<DetailAST> fields = Sets.newHashSet(); 514 515 /** Set of equals calls. */ 516 private final Set<DetailAST> methodCalls = Sets.newHashSet(); 517 518 /** Name of the class, enum or enum constant declaration. */ 519 private String frameName; 520 521 /** Whether the frame is CLASS_DEF, ENUM_DEF or ENUM_CONST_DEF. */ 522 private boolean classOrEnumOrEnumConstDef; 523 524 /** 525 * Creates new frame. 526 * @param parent parent frame. 527 */ 528 FieldFrame(FieldFrame parent) { 529 this.parent = parent; 530 } 531 532 /** 533 * Set the frame name. 534 * @param frameName value to set. 535 */ 536 public void setFrameName(String frameName) { 537 this.frameName = frameName; 538 } 539 540 /** 541 * Getter for the frame name. 542 * @return frame name. 543 */ 544 public String getFrameName() { 545 return frameName; 546 } 547 548 /** 549 * Getter for the parent frame. 550 * @return parent frame. 551 */ 552 public FieldFrame getParent() { 553 return parent; 554 } 555 556 /** 557 * Getter for frame's children. 558 * @return children of this frame. 559 */ 560 public Set<FieldFrame> getChildren() { 561 return Collections.unmodifiableSet(children); 562 } 563 564 /** 565 * Add child frame to this frame. 566 * @param child frame to add. 567 */ 568 public void addChild(FieldFrame child) { 569 children.add(child); 570 } 571 572 /** 573 * Add field to this FieldFrame. 574 * @param field the ast of the field. 575 */ 576 public void addField(DetailAST field) { 577 fields.add(field); 578 } 579 580 /** 581 * Sets isClassOrEnum. 582 * @param value value to set. 583 */ 584 public void setClassOrEnumOrEnumConstDef(boolean value) { 585 classOrEnumOrEnumConstDef = value; 586 } 587 588 /** 589 * Getter for classOrEnumOrEnumConstDef. 590 * @return classOrEnumOrEnumConstDef. 591 */ 592 public boolean isClassOrEnumOrEnumConstDef() { 593 return classOrEnumOrEnumConstDef; 594 } 595 596 /** 597 * Add method call to this frame. 598 * @param methodCall METHOD_CALL ast. 599 */ 600 public void addMethodCall(DetailAST methodCall) { 601 methodCalls.add(methodCall); 602 } 603 604 /** 605 * Determines whether this FieldFrame contains the field. 606 * @param name name of the field to check. 607 * @return true if this FieldFrame contains instance field field. 608 */ 609 public DetailAST findField(String name) { 610 for (DetailAST field: fields) { 611 if (getFieldName(field).equals(name)) { 612 return field; 613 } 614 } 615 return null; 616 } 617 618 /** 619 * Getter for frame's method calls. 620 * @return method calls of this frame. 621 */ 622 public Set<DetailAST> getMethodCalls() { 623 return Collections.unmodifiableSet(methodCalls); 624 } 625 626 /** 627 * Get the name of the field. 628 * @param field to get the name from. 629 * @return name of the field. 630 */ 631 private static String getFieldName(DetailAST field) { 632 return field.findFirstToken(TokenTypes.IDENT).getText(); 633 } 634 } 635}