content: /*
   * Copyright 1999-2017 Alibaba Group Holding Ltd.
   *
   * Licensed under the Apache License, Version 2.0 (the "License");
   * you may not use this file except in compliance with the License.
   * You may obtain a copy of the License at
   *
   *      http://www.apache.org/licenses/LICENSE-2.0
   *
   * Unless required by applicable law or agreed to in writing, software
   * distributed under the License is distributed on an "AS IS" BASIS,
   * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
   * See the License for the specific language governing permissions and
   * limitations under the License.
   */
  package com.alibaba.druid.sql.ast.expr;
  
  import com.alibaba.druid.sql.ast.SQLExprImpl;
  import com.alibaba.druid.sql.ast.SQLObject;
  import com.alibaba.druid.sql.visitor.SQLASTVisitor;
  
  import java.util.Collections;
  import java.util.List;
  
  import static com.alibaba.druid.sql.visitor.SQLEvalVisitor.EVAL_VALUE_NULL;
  
  public final class SQLNullExpr extends SQLExprImpl implements SQLLiteralExpr, SQLValuableExpr {
      public SQLNullExpr() {
      }
  
      public SQLNullExpr(SQLObject parent) {
          this.parent = parent;
      }
  
      public void output(StringBuilder buf) {
          buf.append("NULL");
      }
  
      protected void accept0(SQLASTVisitor visitor) {
          visitor.visit(this);
  
          visitor.endVisit(this);
      }
  
      public int hashCode() {
          return 0;
      }
  
      public boolean equals(Object o) {
          return o instanceof SQLNullExpr;
      }
  
      @Override
      public Object getValue() {
          return EVAL_VALUE_NULL;
      }
  
      public SQLNullExpr clone() {
          return new SQLNullExpr();
      }
  
      @Override
      public List getChildren() {
          return Collections.emptyList();
      }
  }
  