java：接口中的default方法

前言

  在书写moa.evaluation包下的接口文档时，发现java接口中并非所有的方法都是抽象方法。除了抽象方法之外，还有一种用default作为修饰符具体实现的方法。

实例

package moa.evaluation;

import com.yahoo.labs.samoa.instances.Prediction;

import moa.MOAObject;
import moa.capabilities.CapabilitiesHandler;
import moa.capabilities.Capability;
import moa.capabilities.ImmutableCapabilities;
import moa.core.Example;
import moa.core.Measurement;

/**
 * Interface implemented by learner evaluators to monitor
 * the results of the learning process.
 *
 * @author Richard Kirkby (rkirkby@cs.waikato.ac.nz)
 * @version $Revision: 7 $
 */
public interface LearningPerformanceEvaluator<E extends Example> extends MOAObject, CapabilitiesHandler {

    /**
     * Resets this evaluator. It must be similar to
     * starting a new evaluator from scratch.
     *
     */
	public void reset();

   /**
     * Adds a learning result to this evaluator.
     *
     * @param example the example to be classified
     * @param classVotes an array containing the estimated membership
     * probabilities of the test instance in each class
     */
    public void addResult(E example, double[] classVotes);
    public void addResult(E testInst, Prediction prediction);

    /**
     * Gets the current measurements monitored by this evaluator.
     *
     * @return an array of measurements monitored by this evaluator
     */
	public Measurement[] getPerformanceMeasurements();

	@Override
	default ImmutableCapabilities defineImmutableCapabilities() {
	  return new ImmutableCapabilities(Capability.VIEW_STANDARD);
	}

}

  其中，defineImmutableCapabilities()即为用default作为修饰符、具体实现的方法。

  在java8以后，接口中可以添加使用default作为修饰符的方法。使用default作为修饰符的方法，只能在接口中使用，被标记为普通方法，可以直接编写方法体。