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  package com.qulice.pmd.rules;
  
  import java.util.Arrays;
  import java.util.HashMap;
  import java.util.List;
  import java.util.Map;
  import net.sourceforge.pmd.lang.ast.Node;
  import net.sourceforge.pmd.lang.java.ast.ASTExpression;
  import net.sourceforge.pmd.lang.java.ast.ASTMethodDeclaration;
  import net.sourceforge.pmd.lang.java.ast.ASTReferenceType;
  import net.sourceforge.pmd.lang.java.ast.ASTResultType;
  import net.sourceforge.pmd.lang.java.ast.ASTType;
  import net.sourceforge.pmd.lang.java.ast.ASTVariableDeclaratorId;
  import net.sourceforge.pmd.lang.java.ast.JavaNode;
  import net.sourceforge.pmd.lang.java.symboltable.JavaNameOccurrence;
  import net.sourceforge.pmd.lang.java.symboltable.MethodNameDeclaration;
  import net.sourceforge.pmd.lang.symboltable.NameOccurrence;
  import net.sourceforge.pmd.lang.symboltable.Scope;
  
  /**
   * Rule to prohibit use of String.length() when checking for empty string.
   * String.isEmpty() should be used instead.
   * @since 0.18
   */
  @SuppressWarnings("deprecation")
  public final class UseStringIsEmptyRule
      extends net.sourceforge.pmd.lang.java.rule.AbstractInefficientZeroCheck {
  
      @Override
      public boolean appliesToClassName(final String name) {
          return net.sourceforge.pmd.util.StringUtil.isSame(
              name, "String", true, true, true
          );
      }
  
      @Override
      public Map<String, List<String>> getComparisonTargets() {
          final Map<String, List<String>> rules = new HashMap<>();
          rules.put("<", Arrays.asList("1"));
          rules.put(">", Arrays.asList("0"));
          rules.put("==", Arrays.asList("0"));
          rules.put("!=", Arrays.asList("0"));
          rules.put(">=", Arrays.asList("0", "1"));
          rules.put("<=", Arrays.asList("0"));
          return rules;
      }
  
      @Override
      public boolean isTargetMethod(final JavaNameOccurrence occ) {
          final NameOccurrence name = occ.getNameForWhichThisIsAQualifier();
          return name != null && "length".equals(name.getImage());
      }
  
      @Override
      public Object visit(
          final ASTVariableDeclaratorId variable, final Object data
      ) {
          final Node node = variable.getTypeNameNode();
          if (node instanceof ASTReferenceType) {
              final Class<?> clazz = variable.getType();
              final String type = variable.getNameDeclaration().getTypeImage();
              if (clazz != null && !clazz.isArray()
                  && this.appliesToClassName(type)
              ) {
                  final List<NameOccurrence> declarations = variable.getUsages();
                  this.checkDeclarations(declarations, data);
              }
          }
          variable.childrenAccept(this, data);
         return data;
     }
 
     @Override
     public Object visit(
         final ASTMethodDeclaration declaration, final Object data
     ) {
         final ASTResultType result = declaration.getResultType();
         if (!result.isVoid()) {
             final ASTType node = (ASTType) result.jjtGetChild(0);
             final Class<?> clazz = node.getType();
             final String type = node.getTypeImage();
             if (clazz != null && !clazz.isArray()
                 && this.appliesToClassName(type)
             ) {
                 final Scope scope = declaration.getScope().getParent();
                 final MethodNameDeclaration method = new MethodNameDeclaration(
                     declaration.getMethodDeclarator()
                 );
                 final List<NameOccurrence> declarations = scope
                     .getDeclarations(MethodNameDeclaration.class)
                     .get(method);
                 this.checkDeclarations(declarations, data);
             }
         }
         declaration.childrenAccept(this, data);
         return data;
     }
 
     /**
      * Checks all uses of a variable or method with a String type.
      * @param occurrences Variable or method occurrences.
      * @param data Rule context.
      */
     private void checkDeclarations(
         final Iterable<NameOccurrence> occurrences, final Object data
     ) {
         for (final NameOccurrence occurrence : occurrences) {
             final JavaNameOccurrence jocc = (JavaNameOccurrence) occurrence;
             if (this.isTargetMethod(jocc)) {
                 final JavaNode location = jocc.getLocation();
                 final Node expr = location.getFirstParentOfType(
                     ASTExpression.class
                 );
                 this.checkNodeAndReport(
                     data, occurrence.getLocation(), expr.jjtGetChild(0)
                 );
             }
         }
     }
 }