[实例]写一个HashMap的子类，有map.put("ABC","text"),map.get("aBc")，让求输出text

就是让你覆盖 put 和 get 方法

public class C<K,V> extends HashMap<K,V>{
    private static final long serialVersionUID = 1L;
    @Override
    public V put(K key, V value) {
        if(key instanceof String){ 
            key = extracted(key.toString());
        }
        return super.put(key, value);
    }
    private K extracted(String k) {
        return (K) k.toLowerCase();
    }
    @Override
    public V get(Object key) {
        if(key instanceof String){ 
            key = extracted(key.toString());
        }
        return super.get(key);
    }
    
    public static void main(String[] args) {
        Map<String,String> c = new C<String,String>();
        c.put("ABC","text");
        System.out.println(c.get("aBc"));
    }
}