org.apache.flink.util.Visitable Maven / Gradle / Ivy
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* to you under the Apache License, Version 2.0 (the
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* 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
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*/
package org.apache.flink.util;
import org.apache.flink.annotation.Internal;
/**
* This interface marks types as visitable during a traversal. The central method accept(...) contains the logic
* about how to invoke the supplied {@link Visitor} on the visitable object, and how to traverse further.
*
* This concept makes it easy to implement for example a depth-first traversal of a tree or DAG with different types of
* logic during the traversal. The accept(...) method calls the visitor and then send the visitor to its children
* (or predecessors). Using different types of visitors, different operations can be performed during the traversal, while
* writing the actual traversal code only once.
*
* @see Visitor
*/
@Internal
public interface Visitable> {
/**
* Contains the logic to invoke the visitor and continue the traversal.
* Typically invokes the pre-visit method of the visitor, then sends the visitor to the children (or predecessors)
* and then invokes the post-visit method.
*
* A typical code example is the following:
*
{@code
* public void accept(Visitor visitor) {
* boolean descend = visitor.preVisit(this);
* if (descend) {
* if (this.input != null) {
* this.input.accept(visitor);
* }
* visitor.postVisit(this);
* }
* }
* }
*
* @param visitor The visitor to be called with this object as the parameter.
*
* @see Visitor#preVisit(Visitable)
* @see Visitor#postVisit(Visitable)
*/
void accept(Visitor visitor);
}