# Interface CommandVisitor<T>

Type Parameters:
  `T` - object type

All Known Implementing Classes:
  `ReplacementsFinder`

public interface CommandVisitor<T>
Walks through `EditScript` objects.

Users should implement this interface in order to walk through the `EditScript` object created by the comparison of two sequences. This is a direct application of the visitor design pattern. The `EditScript.visit` method takes an object implementing this interface as an argument, it will perform the loop over all commands in the script and the proper methods of the user class will be called as the commands are encountered.

The implementation of the user visitor class will depend on the need. Here are two examples.

The first example is a visitor that build the longest common subsequence:

    import org.apache.commons.text.diff.CommandVisitor;

    import java.util.ArrayList;

    public class LongestCommonSubSequence implements CommandVisitor {

      public LongestCommonSubSequence() {
        a = new ArrayList();
      }

      public void visitInsertCommand(Object object) {
      }

      public void visitKeepCommand(Object object) {
        a.add(object);
      }

      public void visitDeleteCommand(Object object) {
      }

      public Object[] getSubSequence() {
        return a.toArray();
      }

      private ArrayList a;

    }

The second example is a visitor that shows the commands and the way they transform the first sequence into the second one:

    import org.apache.commons.text.diff.CommandVisitor;

    import java.util.Arrays;
    import java.util.ArrayList;
    import java.util.Iterator;

    public class ShowVisitor implements CommandVisitor {

      public ShowVisitor(Object[] sequence1) {
        v = new ArrayList();
        v.addAll(Arrays.asList(sequence1));
        index = 0;
      }

      public void visitInsertCommand(Object object) {
        v.insertElementAt(object, index++);
        display("insert", object);
      }

      public void visitKeepCommand(Object object) {
        ++index;
        display("keep  ", object);
      }

      public void visitDeleteCommand(Object object) {
        v.remove(index);
        display("delete", object);
      }

      private void display(String commandName, Object object) {
        System.out.println(commandName + " " + object + ": " + this);
      }

      public String toString() {
        StringBuffer buffer = new StringBuffer();
        for (Iterator iter = v.iterator(); iter.hasNext();) {
          buffer.append(' ').append(iter.next());
        }
        return buffer.toString();
      }

      private ArrayList v;
      private int index;

    }

Since:
  1.0

- ## Method Summary

  Modifier and Type
  Method
  Description
  `void`
  `visitDeleteCommand(T object)`
  Method called when a delete command is encountered.
  `void`
  `visitInsertCommand(T object)`
  Method called when an insert command is encountered.
  `void`
  `visitKeepCommand(T object)`
  Method called when a keep command is encountered.

- ## Method Details

  - ### visitDeleteCommand

    void visitDeleteCommand(T object)
    Method called when a delete command is encountered.
    Parameters:
      `object` - object to delete (this object comes from the first sequence).

  - ### visitInsertCommand

    void visitInsertCommand(T object)
    Method called when an insert command is encountered.
    Parameters:
      `object` - object to insert (this object comes from the second sequence).

  - ### visitKeepCommand

    void visitKeepCommand(T object)
    Method called when a keep command is encountered.
    Parameters:
      `object` - object to keep (this object comes from the first sequence).