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    <p>A few options:</p> <p>1) One constructor that takes both maps and is safe when passed a null.</p> <pre><code>public MyClass( Map&lt;String, Integer&gt; map1, Map&lt;String, String&gt; map2 ) { if ( map1 != null ) { this.map1 = map1; } if ( map2 != null ) { this.map2 = map2; } } </code></pre> <p>2) Setters for each map</p> <pre><code>public MyClass { private Map&lt;String, Integer&gt; map1; private Map&lt;String, String&gt; map2; public void setMap1( Map&lt;String, Integer&gt; map1 ) { this.map1 = map1; } public void setMap1( Map&lt;String, String&gt; map2 ) { this.map2 = map2; } } </code></pre> <p>3) A builder that allows you to differentiate between the maps and constructs the object properly (calling the setters)</p> <pre><code>public MyClass { private Map&lt;String, Integer&gt; map1; private Map&lt;String, String&gt; map2; // pretend you don't want people to be able to swap out the map after construction so you protect the setter here. protected void setMap1( Map&lt;String, Integer&gt; map1 ) { this.map1 = map1; } protected void setMap1( Map&lt;String, String&gt; map2 ) { this.map2 = map2; } // getters for the maps and other properties public static Builder builder() { return new Builder(); } public static class Builder { private Map&lt;String, Integer&gt; map1; private Map&lt;String, String&gt; map2; public Builder withMap1( Map&lt;String, Integer&gt; map ) { map1 = map; return this; } public Builder withMap2( Map&lt;String, String&gt; map ) { map2 = map; return this; } public MyClass build() { MyClass c = new MyClass(); // possibly conditional code that inspects the maps for specific values or validity c.setMap1( map1 ); c.setMap2( map2 ); // initialization of other fields return c; } } public static void main( String[] args ) { // sample usage MyClass instance1 = MyClass.builder().withMap1(myMap1).build(); MyClass instance2 = MyClass.builder().withMap2(myMap2).build(); MyClass instance3 = MyClass.builder().withMap1(myMap1).withMap2(myMap2).build(); } } </code></pre> <p>4) Static factory (as pointed out by Evgeniy Dorofeev below)</p> <pre><code>public MyClass { private Map&lt;String, Integer&gt; map1; private Map&lt;String, String&gt; map2; // other properties private MyClass() {} public static MyClass withMap1(Map&lt;String, Integer&gt; map ) { MyClass c = new MyClass(); c.map1 = map; return c; } public static MyClass withMap2(Map&lt;String, String&gt; map ) { MyClass c = new MyClass(); c.map2 = map; return c; } // getters and setters } </code></pre>
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    1. POHow to define 2 constructors with 2 different type of HashMaps?
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    1. USdigitaljoel
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    1. POHow to define 2 constructors with 2 different type of HashMaps?
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    1. COExcellent answer. It provides a workaround to the problem. +1
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      1. USJoseph Carrigan
    2. COI don't understand why you check for `null` in the first solution. AFAIK assigning `null` shouldn't create any error, and at that point in the code `this.mapX` are `null`s which means that assigning `null` wont change a thing. I could understand that if there was an `else` initializing the `mapX` attribute to a new empty hash-map, but as it stands those `if` seem pretty useless. Or am I wrong?
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    3. COIn this case, yes, the null check is redundant, but I put it in there simply to demonstrate that they can do whatever they want. Perhaps at declaration (which isn't shown in the code sample) they are initializing map1 and map2 to an empty hashmap so they don't have to do null checks elsewhere. Then the null check makes sense in the constructor so as not to override the default value.
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