src/main/java/org/mockito/internal/stubbing/defaultanswers/ReturnsEmptyValues.java

/*
 * Copyright (c) 2007 Mockito contributors
 * This program is made available under the terms of the MIT License.
 */

package org.mockito.internal.stubbing.defaultanswers;

import org.mockito.internal.util.MockUtil;
import org.mockito.internal.util.ObjectMethodsGuru;
import org.mockito.internal.util.Primitives;
import org.mockito.invocation.InvocationOnMock;
import org.mockito.mock.MockName;
import org.mockito.stubbing.Answer;

import java.io.Serializable;
import java.util.ArrayList;
import java.util.Collection;
import java.util.HashMap;
import java.util.HashSet;
import java.util.LinkedHashMap;
import java.util.LinkedHashSet;
import java.util.LinkedList;
import java.util.List;
import java.util.Map;
import java.util.Set;
import java.util.SortedMap;
import java.util.SortedSet;
import java.util.TreeMap;
import java.util.TreeSet;

/**
 * Default answer of every Mockito mock.
 * <ul>
 * <li>
 *  Returns appropriate primitive for primitive-returning methods
 * </li>
 * <li>
 *  Returns consistent values for primitive wrapper classes (e.g. int-returning method retuns 0 <b>and</b> Integer-returning method returns 0, too)
 * </li>
 * <li>
 *  Returns empty collection for collection-returning methods (works for most commonly used collection types)
 * </li>
 * <li>
 *  Returns description of mock for toString() method
 * </li>
 * <li>
 *  Returns zero if references are equals otherwise non-zero for Comparable#compareTo(T other) method (see issue 184)
 * </li>
 * <li>
 *  Returns null for everything else
 * </li>
 * </ul>
 */
public class ReturnsEmptyValues implements Answer<Object>, Serializable {
    
    private static final long serialVersionUID = 1998191268711234347L;
    ObjectMethodsGuru methodsGuru = new ObjectMethodsGuru();
    MockUtil mockUtil = new MockUtil();

    /* (non-Javadoc)
     * @see org.mockito.stubbing.Answer#answer(org.mockito.invocation.InvocationOnMock)
     */
    public Object answer(InvocationOnMock invocation) {
        if (methodsGuru.isToString(invocation.getMethod())) {
            Object mock = invocation.getMock();
            MockName name = mockUtil.getMockName(mock);
            if (name.isDefault()) {
                return "Mock for " + mockUtil.getMockSettings(mock).getTypeToMock().getSimpleName() + ", hashCode: " + mock.hashCode();
            } else {
                return name.toString();
            }
        } else if (methodsGuru.isCompareToMethod(invocation.getMethod())) {
            //see issue 184.
            //mocks by default should return 0 if references are the same, otherwise some other value because they are not the same. Hence we return 1 (anything but 0 is good).
            //Only for compareTo() method by the Comparable interface
            return invocation.getMock() == invocation.getArguments()[0] ? 0 : 1;
        }
        
        Class<?> returnType = invocation.getMethod().getReturnType();
        return returnValueFor(returnType);
    }
    
    Object returnValueFor(Class<?> type) {
        if (Primitives.isPrimitiveOrWrapper(type)) {
            return Primitives.defaultValueForPrimitiveOrWrapper(type);
        //new instances are used instead of Collections.emptyList(), etc.
        //to avoid UnsupportedOperationException if code under test modifies returned collection
        } else if (type == Collection.class) {
            return new LinkedList<Object>();
        } else if (type == Set.class) {
            return new HashSet<Object>();
        } else if (type == HashSet.class) {
            return new HashSet<Object>();
        } else if (type == SortedSet.class) {
            return new TreeSet<Object>();
        } else if (type == TreeSet.class) {
            return new TreeSet<Object>();
        } else if (type == LinkedHashSet.class) {
            return new LinkedHashSet<Object>();
        } else if (type == List.class) {
            return new LinkedList<Object>();
        } else if (type == LinkedList.class) {
            return new LinkedList<Object>();
        } else if (type == ArrayList.class) {
            return new ArrayList<Object>();
        } else if (type == Map.class) {
            return new HashMap<Object, Object>();
        } else if (type == HashMap.class) {
            return new HashMap<Object, Object>();
        } else if (type == SortedMap.class) {
            return new TreeMap<Object, Object>();
        } else if (type == TreeMap.class) {
            return new TreeMap<Object, Object>();
        } else if (type == LinkedHashMap.class) {
            return new LinkedHashMap<Object, Object>();
        }
        // TODO return empty Iterable ; see issue 175

        //Let's not care about the rest of collections.
        return null;
    }

}