我有一个带有2个HashMap字段的类,如下所示:
HashMap<String, Integer> map1;
HashMap<String, String> map2;
现在,我只想在构造函数中传递其中一个映射,即map1或map2类型。但是,我无法使用不同类型的HashMap定义2个不同的构造函数。这是解决方法吗?
最佳答案
一些选择:
1)一个构造函数同时获取两个映射,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 map 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)构建器,可让您区分 map 并正确构建对象(调用 setter )
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(如以下Evgeniy Dorofeev所指出的)
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
}