code: /*
   * #%L
   * Simmetrics Core
   * %%
   * Copyright (C) 2014 - 2016 Simmetrics Authors
   * %%
   * 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.
   * #L%
   */
  package org.simmetrics.metrics;
  
  import static com.google.common.base.Preconditions.checkNotNull;
  
  import org.simmetrics.Distance;
  import org.simmetrics.Metric;
  
  /**
   * Identity similarity and distance metric that returns a distance of 0.0 and
   * similarity 1.0 when the inputs are equals, and vice-versa when they're not.
   * <p>
   * <code>
   * similarity(a,b) = equals(a,b) ? 1.0f : 0.0f
   * <br>
   * distance(a,b) = equals(a,b) ? 0.0f : 1.0f
   * </code>
   * <p>
   * This class is immutable and thread-safe.
   * 
   * @param <T>
   *            type of token
   */
  public final class Identity<T> implements Metric<T>, Distance<T> {
  
  	@Override
  	public float compare(T a, T b) {
  		checkNotNull(a);
  		checkNotNull(b);
  		return a.equals(b) ? 1.0f : 0.0f;
  	}
  	
  	@Override
  	public float distance(T a, T b) {
  		checkNotNull(a);
  		checkNotNull(b);
  		return a.equals(b) ? 0.0f : 1.0f;
  	}
  	
  	@Override
  	public String toString() {
  		return "Identity";
  	}
  }
  