[英]how do i preload a hashmap in an object(without put method)?
I have a class and it has a couple data structures in it among which is a hashmap. 我有一个类,它有几个数据结构,其中是一个hashmap。 But I want the hashmap to have default values so I need to preload it. 但是我希望hashmap具有默认值,所以我需要预加载它。 How do I do this since I can't use put method inside the object? 我怎么做这个因为我不能在对象里面使用put方法?
class Profile
{
HashMap closedAges = new HashMap();
closedAges.put("19");
}
I fixed it with this but I had to use a method within the object. 我用它修复了它,但我不得不在对象中使用一个方法。
class Profile
{
HashMap closedAges = loadAges();
HashMap loadAges()
{
HashMap closedAges = new HashMap();
String[] ages = {"19", "46", "54", "56", "83"};
for (String age : ages)
{
closedAges.put(age, false);
}
return closedAges;
}
}
You want to do this in the constructor of your class, for instance 例如,您希望在类的构造函数中执行此操作
class Example {
Map<Integer, String> data = new HashMap<>();
public Example() {
data.put(1, "Hello");
data.put(2, "World");
}
}
or to use the freakish double brace initialization feature of Java: 或者使用Java的奇特双括号初始化功能:
class Example {
Map<Integer, String> data;
public Example() {
/* here the generic type parameters cannot be omitted */
data = new HashMap<Integer, String>() {{
put(1, "Hello");
put(2, "World");
}};
}
}
And finally, if your HashMap
is a static field of your class, you can perform the initialization inside a static
block: 最后,如果您的HashMap
是类的静态字段,则可以在static
块内执行初始化:
static {
data.put(1, "Hello");
...
}
In order to address Behes comment, if you are not using Java 7, fill the <>
brackets with your type parameters, in this case <Integer, String>
. 为了解决Behes注释,如果您不使用Java 7,请使用类型参数填充<>
括号,在本例中为<Integer, String>
。
You could do this: 你可以这样做:
Map<String, String> map = new HashMap<String, String>() {{
put("1", "one");
put("2", "two");
put("3", "three");
}};
This java idiom is called double brace initialization .: 这个java习语称为双括号初始化 。:
The first brace creates a new AnonymousInnerClass, the second declares an instance initializer block that is run when the anonymous inner class is instantiated. 第一个大括号创建一个新的AnonymousInnerClass,第二个大括号声明在实例化匿名内部类时运行的实例初始化程序块。
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