OuterBakedGoodsMap4.putAll(actualBakedGoodsMap) ĪssertEquals(actualBakedGoodsMap, outerBakedGoodsMap4) ĪssertEquals(actualEmployeeMap, employeeMap1) 6. For a user-defined map, if all identical objects are moved into another map, the equality check succeeds: Map> outerBakedGoodsMap4 = new HashMap() If both the maps are the same, then the equality check succeeds. Map> expectedMap = setupAddressObjectMap() ĪssertNotSame(expectedMap, actualEmployeeMap) ĪssertNotEquals(expectedMap, actualEmployeeMap) Otherwise, the checks will fail: //Comparing a Map> and Map> mapĪssertNotSame(employeeMap1, actualEmployeeMap) ĪssertNotEquals(employeeMap1, actualEmployeeMap) Map> employeeAddressMap1 = mUtil.createNestedMapfromStream(listEmployee) ĪssertNotEquals(employeeAddressMap1, actualEmployeeAddressMap) įor the Map with user-defined objects as values, we need to customize the equality method using one of the methods mentioned in the comparing HashMaps article. OuterBakedGoodsMap3.put("Donut", mUtil.buildInnerMap(batterList)) ĪssertNotEquals(outerBakedGoodsMap2, actualBakedGoodsMap) Similarly, if we change the outer Map‘s contents, the equality check will fail as well: assertNotEquals(outerBakedGoodsMap2, actualBakedGoodsMap) If the inner objects are all new instances every time in the case of user-defined objects, the equality check will also fail. If we change the inner Map's contents, the equality check fails. The default implementation compares each value. We can compare them using the equals() method. There are many ways to compare HashMaps in Java. In the second example, we are building an object of type >: Map> employeeMap = new HashMap() ĮmployeeMap = listEmployee.stream().collect(oupingBy((Employee emp) -> emp.getEmployeeId(),Ĭollectors.toMap((Employee emp) -> emp.getAddress().getAddressId(), fEmpObj -> fEmpObj.getAddress()))) collect(oupingBy(e -> e.getAddress().getAddressId(),Ĭollectors.toMap(f -> f.getAddress().getAddressLocation(), Employee::getEmployeeName))) Let's have a closer look at a few of these. Since these are all sets, similar iteration principles apply to all of them. Simply put, we can extract the contents of a Map using entrySet (), keySet (), or values (). We're then building a nested HashMap: Map> employeeAddressMap = listEmployee.stream() Overview In this quick tutorial, we'll look at the different ways of iterating through the entries of a Map in Java. In the first example, the Employee has the Address object nested inside it. Here, we have two examples: one has an inner Map of Strings, and the other is a Map with Integer and Object values. Map has provided methods to get only keys or values by invoking methods keyset() and values().įor (String interfaceName : hashMap.If we have a List that we want to convert to a Map, we can create a stream and then convert it to a Map using the Collectors.toMap method. In these type of situations, we'll try to minimize getting entire key-value pair. Might need to get the only keys some scenario where values are not This methodology is commonly used by all programmers if want to retrieve both key and value at the same time. Key(Interface) = Map, Value(Implementation class) = HashMap Key(Interface) = List, Value(Implementation class) = ArrayList Key(Interface) = Set, Value(Implementation class) = Hashset ("Key(Interface) = " + entry.getKey() + ", Value(Implementation class) = " + entry.getValue()) įirst, retrieving the each object from set in the form of entry object and then next calling getKey() to get the key from Node/Entry object and getValue() method to get the value of the corresponding key. See the code below.įor (Map.Entry entry : hashMap.entrySet()) Now we will iterate through enhanced for loop this set. In our case, it is Set> and this holds Entry objects. Map has a method entryset() which returns the Set object. All these values are stored in set in the form of Node which is an Map.Entry object. In all examples today will be executed on the below input. HashMap creates internally Hashset and added Entry objects into Hashset. We must know about internals of how hashmap works in java. As all of us know, ArrayList is directly iterated using Iterator but it is not possible encase of Map because Map is not under Collection interface.
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