001//////////////////////////////////////////////////////////////////////////////// 002// checkstyle: Checks Java source code for adherence to a set of rules. 003// Copyright (C) 2001-2018 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.HashSet; 024import java.util.Set; 025 026import com.puppycrawl.tools.checkstyle.FileStatefulCheck; 027import com.puppycrawl.tools.checkstyle.api.AbstractCheck; 028import com.puppycrawl.tools.checkstyle.api.DetailAST; 029import com.puppycrawl.tools.checkstyle.api.TokenTypes; 030 031/** 032 * Checks that any combination of String literals 033 * is on the left side of an equals() comparison. 034 * Also checks for String literals assigned to some field 035 * (such as {@code someString.equals(anotherString = "text")}). 036 * 037 * <p>Rationale: Calling the equals() method on String literals 038 * will avoid a potential NullPointerException. Also, it is 039 * pretty common to see null check right before equals comparisons 040 * which is not necessary in the below example. 041 * 042 * <p>For example: 043 * 044 * <pre> 045 * {@code 046 * String nullString = null; 047 * nullString.equals("My_Sweet_String"); 048 * } 049 * </pre> 050 * should be refactored to 051 * 052 * <pre> 053 * {@code 054 * String nullString = null; 055 * "My_Sweet_String".equals(nullString); 056 * } 057 * </pre> 058 * 059 */ 060@FileStatefulCheck 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 getRequiredTokens(); 090 } 091 092 @Override 093 public int[] getAcceptableTokens() { 094 return getRequiredTokens(); 095 } 096 097 @Override 098 public int[] getRequiredTokens() { 099 return new int[] { 100 TokenTypes.METHOD_CALL, 101 TokenTypes.CLASS_DEF, 102 TokenTypes.METHOD_DEF, 103 TokenTypes.LITERAL_IF, 104 TokenTypes.LITERAL_FOR, 105 TokenTypes.LITERAL_WHILE, 106 TokenTypes.LITERAL_DO, 107 TokenTypes.LITERAL_CATCH, 108 TokenTypes.LITERAL_TRY, 109 TokenTypes.VARIABLE_DEF, 110 TokenTypes.PARAMETER_DEF, 111 TokenTypes.CTOR_DEF, 112 TokenTypes.SLIST, 113 TokenTypes.ENUM_DEF, 114 TokenTypes.ENUM_CONSTANT_DEF, 115 TokenTypes.LITERAL_NEW, 116 }; 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.findFirstToken(TokenTypes.OBJBLOCK) != null) { 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. 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.findFirstToken(TokenTypes.OBJBLOCK) != null) { 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 child.getMethodCalls().forEach(this::checkMethodCall); 262 } 263 } 264 265 /** 266 * Check whether the method call should be violated. 267 * @param methodCall method call to check. 268 */ 269 private void checkMethodCall(DetailAST methodCall) { 270 DetailAST objCalledOn = methodCall.getFirstChild().getFirstChild(); 271 if (objCalledOn.getType() == TokenTypes.DOT) { 272 objCalledOn = objCalledOn.getLastChild(); 273 } 274 final DetailAST expr = methodCall.findFirstToken(TokenTypes.ELIST).getFirstChild(); 275 if (isObjectValid(objCalledOn) 276 && containsOneArgument(methodCall) 277 && containsAllSafeTokens(expr) 278 && isCalledOnStringFieldOrVariable(objCalledOn)) { 279 final String methodName = methodCall.getFirstChild().getLastChild().getText(); 280 if (EQUALS.equals(methodName)) { 281 log(methodCall, MSG_EQUALS_AVOID_NULL); 282 } 283 else { 284 log(methodCall, MSG_EQUALS_IGNORE_CASE_AVOID_NULL); 285 } 286 } 287 } 288 289 /** 290 * Check whether the object equals method is called on is not a String literal 291 * and not too complex. 292 * @param objCalledOn the object equals method is called on ast. 293 * @return true if the object is valid. 294 */ 295 private static boolean isObjectValid(DetailAST objCalledOn) { 296 boolean result = true; 297 final DetailAST previousSibling = objCalledOn.getPreviousSibling(); 298 if (previousSibling != null 299 && previousSibling.getType() == TokenTypes.DOT) { 300 result = false; 301 } 302 if (isStringLiteral(objCalledOn)) { 303 result = false; 304 } 305 return result; 306 } 307 308 /** 309 * Checks for calling equals on String literal and 310 * anon object which cannot be null. 311 * @param objCalledOn object AST 312 * @return if it is string literal 313 */ 314 private static boolean isStringLiteral(DetailAST objCalledOn) { 315 return objCalledOn.getType() == TokenTypes.STRING_LITERAL 316 || objCalledOn.getType() == TokenTypes.LITERAL_NEW; 317 } 318 319 /** 320 * Verify that method call has one argument. 321 * 322 * @param methodCall METHOD_CALL DetailAST 323 * @return true if method call has one argument. 324 */ 325 private static boolean containsOneArgument(DetailAST methodCall) { 326 final DetailAST elist = methodCall.findFirstToken(TokenTypes.ELIST); 327 return elist.getChildCount() == 1; 328 } 329 330 /** 331 * Looks for all "safe" Token combinations in the argument 332 * expression branch. 333 * @param expr the argument expression 334 * @return - true if any child matches the set of tokens, false if not 335 */ 336 private static boolean containsAllSafeTokens(final DetailAST expr) { 337 DetailAST arg = expr.getFirstChild(); 338 arg = skipVariableAssign(arg); 339 340 boolean argIsNotNull = false; 341 if (arg.getType() == TokenTypes.PLUS) { 342 DetailAST child = arg.getFirstChild(); 343 while (child != null 344 && !argIsNotNull) { 345 argIsNotNull = child.getType() == TokenTypes.STRING_LITERAL 346 || child.getType() == TokenTypes.IDENT; 347 child = child.getNextSibling(); 348 } 349 } 350 351 return argIsNotNull 352 || !arg.branchContains(TokenTypes.IDENT) 353 && !arg.branchContains(TokenTypes.LITERAL_NULL); 354 } 355 356 /** 357 * Skips over an inner assign portion of an argument expression. 358 * @param currentAST current token in the argument expression 359 * @return the next relevant token 360 */ 361 private static DetailAST skipVariableAssign(final DetailAST currentAST) { 362 DetailAST result = currentAST; 363 if (currentAST.getType() == TokenTypes.ASSIGN 364 && currentAST.getFirstChild().getType() == TokenTypes.IDENT) { 365 result = currentAST.getFirstChild().getNextSibling(); 366 } 367 return result; 368 } 369 370 /** 371 * Determine, whether equals method is called on a field of String type. 372 * @param objCalledOn object ast. 373 * @return true if the object is of String type. 374 */ 375 private boolean isCalledOnStringFieldOrVariable(DetailAST objCalledOn) { 376 final boolean result; 377 final DetailAST previousSiblingAst = objCalledOn.getPreviousSibling(); 378 if (previousSiblingAst == null) { 379 result = isStringFieldOrVariable(objCalledOn); 380 } 381 else { 382 if (previousSiblingAst.getType() == TokenTypes.LITERAL_THIS) { 383 result = isStringFieldOrVariableFromThisInstance(objCalledOn); 384 } 385 else { 386 final String className = previousSiblingAst.getText(); 387 result = isStringFieldOrVariableFromClass(objCalledOn, className); 388 } 389 } 390 return result; 391 } 392 393 /** 394 * Whether the field or the variable is of String type. 395 * @param objCalledOn the field or the variable to check. 396 * @return true if the field or the variable is of String type. 397 */ 398 private boolean isStringFieldOrVariable(DetailAST objCalledOn) { 399 boolean result = false; 400 final String name = objCalledOn.getText(); 401 FieldFrame frame = currentFrame; 402 while (frame != null) { 403 final DetailAST field = frame.findField(name); 404 if (field != null 405 && (frame.isClassOrEnumOrEnumConstDef() 406 || checkLineNo(field, objCalledOn))) { 407 result = STRING.equals(getFieldType(field)); 408 break; 409 } 410 frame = frame.getParent(); 411 } 412 return result; 413 } 414 415 /** 416 * Whether the field or the variable from THIS instance is of String type. 417 * @param objCalledOn the field or the variable from THIS instance to check. 418 * @return true if the field or the variable from THIS instance is of String type. 419 */ 420 private boolean isStringFieldOrVariableFromThisInstance(DetailAST objCalledOn) { 421 boolean result = false; 422 final String name = objCalledOn.getText(); 423 final DetailAST field = getObjectFrame(currentFrame).findField(name); 424 if (field != null) { 425 result = STRING.equals(getFieldType(field)); 426 } 427 return result; 428 } 429 430 /** 431 * Whether the field or the variable from the specified class is of String type. 432 * @param objCalledOn the field or the variable from the specified class to check. 433 * @param className the name of the class to check in. 434 * @return true if the field or the variable from the specified class is of String type. 435 */ 436 private boolean isStringFieldOrVariableFromClass(DetailAST objCalledOn, 437 final String className) { 438 boolean result = false; 439 final String name = objCalledOn.getText(); 440 FieldFrame frame = getObjectFrame(currentFrame); 441 while (frame != null) { 442 if (className.equals(frame.getFrameName())) { 443 final DetailAST field = frame.findField(name); 444 if (field != null) { 445 result = STRING.equals(getFieldType(field)); 446 } 447 break; 448 } 449 frame = getObjectFrame(frame.getParent()); 450 } 451 return result; 452 } 453 454 /** 455 * Get the nearest parent frame which is CLASS_DEF, ENUM_DEF or ENUM_CONST_DEF. 456 * @param frame to start the search from. 457 * @return the nearest parent frame which is CLASS_DEF, ENUM_DEF or ENUM_CONST_DEF. 458 */ 459 private static FieldFrame getObjectFrame(FieldFrame frame) { 460 FieldFrame objectFrame = frame; 461 while (objectFrame != null && !objectFrame.isClassOrEnumOrEnumConstDef()) { 462 objectFrame = objectFrame.getParent(); 463 } 464 return objectFrame; 465 } 466 467 /** 468 * Check whether the field is declared before the method call in case of 469 * methods and initialization blocks. 470 * @param field field to check. 471 * @param objCalledOn object equals method called on. 472 * @return true if the field is declared before the method call. 473 */ 474 private static boolean checkLineNo(DetailAST field, DetailAST objCalledOn) { 475 boolean result = false; 476 // Required for pitest coverage. We should specify columnNo passing condition 477 // in such a way, so that the minimal possible distance between field and 478 // objCalledOn will be the maximal condition to pass this check. 479 // The minimal distance between objCalledOn and field (of type String) initialization 480 // is calculated as follows: 481 // String(6) + space(1) + variableName(1) + assign(1) + 482 // anotherStringVariableName(1) + semicolon(1) = 11 483 // Example: length of "String s=d;" is 11 symbols. 484 final int minimumSymbolsBetween = 11; 485 if (field.getLineNo() < objCalledOn.getLineNo() 486 || field.getLineNo() == objCalledOn.getLineNo() 487 && field.getColumnNo() + minimumSymbolsBetween <= objCalledOn.getColumnNo()) { 488 result = true; 489 } 490 return result; 491 } 492 493 /** 494 * Get field type. 495 * @param field to get the type from. 496 * @return type of the field. 497 */ 498 private static String getFieldType(DetailAST field) { 499 String fieldType = null; 500 final DetailAST identAst = field.findFirstToken(TokenTypes.TYPE) 501 .findFirstToken(TokenTypes.IDENT); 502 if (identAst != null) { 503 fieldType = identAst.getText(); 504 } 505 return fieldType; 506 } 507 508 /** 509 * Holds the names of fields of a type. 510 */ 511 private static class FieldFrame { 512 513 /** Parent frame. */ 514 private final FieldFrame parent; 515 516 /** Set of frame's children. */ 517 private final Set<FieldFrame> children = new HashSet<>(); 518 519 /** Set of fields. */ 520 private final Set<DetailAST> fields = new HashSet<>(); 521 522 /** Set of equals calls. */ 523 private final Set<DetailAST> methodCalls = new HashSet<>(); 524 525 /** Name of the class, enum or enum constant declaration. */ 526 private String frameName; 527 528 /** Whether the frame is CLASS_DEF, ENUM_DEF or ENUM_CONST_DEF. */ 529 private boolean classOrEnumOrEnumConstDef; 530 531 /** 532 * Creates new frame. 533 * @param parent parent frame. 534 */ 535 FieldFrame(FieldFrame parent) { 536 this.parent = parent; 537 } 538 539 /** 540 * Set the frame name. 541 * @param frameName value to set. 542 */ 543 public void setFrameName(String frameName) { 544 this.frameName = frameName; 545 } 546 547 /** 548 * Getter for the frame name. 549 * @return frame name. 550 */ 551 public String getFrameName() { 552 return frameName; 553 } 554 555 /** 556 * Getter for the parent frame. 557 * @return parent frame. 558 */ 559 public FieldFrame getParent() { 560 return parent; 561 } 562 563 /** 564 * Getter for frame's children. 565 * @return children of this frame. 566 */ 567 public Set<FieldFrame> getChildren() { 568 return Collections.unmodifiableSet(children); 569 } 570 571 /** 572 * Add child frame to this frame. 573 * @param child frame to add. 574 */ 575 public void addChild(FieldFrame child) { 576 children.add(child); 577 } 578 579 /** 580 * Add field to this FieldFrame. 581 * @param field the ast of the field. 582 */ 583 public void addField(DetailAST field) { 584 fields.add(field); 585 } 586 587 /** 588 * Sets isClassOrEnum. 589 * @param value value to set. 590 */ 591 public void setClassOrEnumOrEnumConstDef(boolean value) { 592 classOrEnumOrEnumConstDef = value; 593 } 594 595 /** 596 * Getter for classOrEnumOrEnumConstDef. 597 * @return classOrEnumOrEnumConstDef. 598 */ 599 public boolean isClassOrEnumOrEnumConstDef() { 600 return classOrEnumOrEnumConstDef; 601 } 602 603 /** 604 * Add method call to this frame. 605 * @param methodCall METHOD_CALL ast. 606 */ 607 public void addMethodCall(DetailAST methodCall) { 608 methodCalls.add(methodCall); 609 } 610 611 /** 612 * Determines whether this FieldFrame contains the field. 613 * @param name name of the field to check. 614 * @return true if this FieldFrame contains instance field field. 615 */ 616 public DetailAST findField(String name) { 617 DetailAST resultField = null; 618 for (DetailAST field: fields) { 619 if (getFieldName(field).equals(name)) { 620 resultField = field; 621 break; 622 } 623 } 624 return resultField; 625 } 626 627 /** 628 * Getter for frame's method calls. 629 * @return method calls of this frame. 630 */ 631 public Set<DetailAST> getMethodCalls() { 632 return Collections.unmodifiableSet(methodCalls); 633 } 634 635 /** 636 * Get the name of the field. 637 * @param field to get the name from. 638 * @return name of the field. 639 */ 640 private static String getFieldName(DetailAST field) { 641 return field.findFirstToken(TokenTypes.IDENT).getText(); 642 } 643 644 } 645 646}