content: package com.alibaba.qlexpress4.runtime.instruction;
  
  import com.alibaba.qlexpress4.QLOptions;
  import com.alibaba.qlexpress4.exception.ErrorReporter;
  import com.alibaba.qlexpress4.exception.QLErrorCodes;
  import com.alibaba.qlexpress4.runtime.*;
  import com.alibaba.qlexpress4.runtime.data.DataValue;
  import com.alibaba.qlexpress4.utils.PrintlnUtils;
  
  import java.util.function.Consumer;
  
  /**
   * Operation: get specified field of object on the top of stack
   * Input: 1
   * Output: 1
   * <p>
   * Author: DQinYuan
   */
  public class GetFieldInstruction extends QLInstruction {
      
      private final String fieldName;
      
      private final boolean optional;
      
      public GetFieldInstruction(ErrorReporter errorReporter, String fieldName, boolean optional) {
          super(errorReporter);
          this.fieldName = fieldName;
          this.optional = optional;
      }
      
      @Override
      public QResult execute(QContext qContext, QLOptions qlOptions) {
          Object bean = qContext.pop().get();
          if (bean == null) {
              if (qlOptions.isAvoidNullPointer() || optional) {
                  qContext.push(DataValue.NULL_VALUE);
                  return QResult.NEXT_INSTRUCTION;
              }
              throw errorReporter.report(new NullPointerException(),
                  QLErrorCodes.NULL_FIELD_ACCESS.name(),
                  QLErrorCodes.NULL_FIELD_ACCESS.getErrorMsg());
          }
          Value fieldValue = qContext.getReflectLoader().loadField(bean, fieldName, false, errorReporter);
          if (fieldValue == null) {
              throw errorReporter.reportFormat(QLErrorCodes.FIELD_NOT_FOUND.name(),
                  QLErrorCodes.FIELD_NOT_FOUND.getErrorMsg(),
                  fieldName);
          }
          qContext.push(fieldValue);
          return QResult.NEXT_INSTRUCTION;
      }
      
      @Override
      public int stackInput() {
          return 1;
      }
      
      @Override
      public int stackOutput() {
          return 1;
      }
      
      @Override
      public void println(int index, int depth, Consumer<String> debug) {
          PrintlnUtils.printlnByCurDepth(depth, index + ": GetField " + fieldName, debug);
      }
      
      public String getFieldName() {
          return fieldName;
      }
      
  }
  