如何定义 2 个具有 2 种不同类型的 HashMap 的构造函数？

几个选项：

1） 一个构造函数，它同时接受两个映射，并且在传递 null 时是安全的。

public MyClass( Map<String, Integer> map1, Map<String, String> map2 ) {
    if ( map1 != null ) { this.map1 = map1; }
    if ( map2 != null ) { this.map2 = map2; }
}

2） 每张地图的二传手

public MyClass {
    private Map<String, Integer> map1;
    private Map<String, String> map2;
    public void setMap1( Map<String, Integer> map1 ) {
        this.map1 = map1;
    }
    public void setMap2( Map<String, String> map2 ) {
        this.map2 = map2;
    }
}

3）一个构建器，允许您区分映射并正确构造对象（调用设置者）

public MyClass {
    private Map<String, Integer> map1;
    private Map<String, String>  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<String, Integer> map1 ) {
        this.map1 = map1;
    }
    protected void setMap1( Map<String, String> map2 ) {
        this.map2 = map2;
    }
    // getters for the maps and other properties
    public static Builder builder() {
        return new Builder();
    }
    public static class Builder {
        private Map<String, Integer> map1;
        private Map<String, String> map2;
        public Builder withMap1( Map<String, Integer> map ) {
            map1 = map;
            return this;
        }
        public Builder withMap2( Map<String, String> 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();
    }
}

4）静态工厂（正如叶甫根尼·多罗菲耶夫在下面指出的那样）

public MyClass {
    private Map<String, Integer> map1;
    private Map<String, String> map2;
    // other properties

    private MyClass() {}

    public static MyClass withMap1(Map<String, Integer> map ) {
        MyClass c = new MyClass();
        c.map1 = map;
        return c;
    }
    public static MyClass withMap2(Map<String, String> map ) {
        MyClass c = new MyClass();
        c.map2 = map;
        return c;
    }
    // getters and setters
}

你不能：泛型在编译阶段被剥离：编译后的代码在这两种情况下都可以看到。HashMap<Object, Object>

此过程的技术名称是类型擦除。查看 http://docs.oracle.com/javase/tutorial/java/generics/erasure.html

在许多方面，这使得Java泛型不如C++模板。