[英]How to use put() in a subclass of Java's TreeMap
I want to create a subclass of class of java.util.TreeMap, to allow me to add an increment method: 我想创建一个java.util.TreeMap类的子类,以允许我添加一个increment方法:
public class CustomTreeMap<K, V> extends TreeMap<K, V> {
public void increment(Integer key) {
Integer intValue;
if (this.containsKey(key)) {
Object value = this.get(key);
if (!(value instanceof Integer)) {
// Fail gracefully
return;
} else {
intValue = (Integer) value;
intValue++;
}
} else {
intValue = 1;
}
this.put(key, intValue); // put(Integer, Integer) cannot be applied in TreeMap
}
}
Android Studio 1.0.2 first proposes put(K Key, V Value)
for autocompletion, and later warns that: Android Studio 1.0.2首先提出
put(K Key, V Value)
用于自动完成,后来警告:
put(K, V) cannot be applied in TreeMap to (java.lang.integer, java.lang.integer)
What is it that I am doing wrong? 我做错了什么?
If you want to create your custom treemap to handle Integers
exclusively, you should make it extend TreeMap<K, Integer>
, not the generic type V
: 如果要创建自定义树形图以独占处理
Integers
,则应使其扩展TreeMap<K, Integer>
,而不是泛型类型V
:
public class CustomTreeMap<K> extends TreeMap<K, Integer> {
...
}
This way you don't need the instanceof
check later. 这样您以后就不需要执行
instanceof
检查。
If your key also needs to be an Integer
, declare no generic types instead: 如果您的密钥也需要是
Integer
,则不要声明泛型类型:
public class CustomTreeMap extends TreeMap<Integer, Integer> {
...
}
If it should be Integer then use Integer: 如果它应该是Integer,那么使用Integer:
public class CustomTreeMap<K> extends TreeMap<K, Integer> {
public void increment(K key) {
Integer intValue;
if (this.containsKey(key)) {
Object value = this.get(key);
if (!(value instanceof Integer)) {
// Fail gracefully
return;
} else {
intValue = (Integer) value;
intValue++;
}
} else {
intValue = 1;
}
this.put(key, intValue); // put(Integer, Integer) cannot be applied in TreeMap
}
}
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