java类型强转为泛型V，竟然没有报错？

Question

public class StrictMap<V> extends HashMap<String, V> {

    private static final long serialVersionUID = -3455861209780003757L;

    private String name;

    public StrictMap(int initialCapacity, float loadFactor, String name) {
        super(initialCapacity, loadFactor);
        this.name = name;
    }

    public StrictMap(int initialCapacity, String name) {
        super(initialCapacity);
        this.name = name;
    }

    public StrictMap(String name) {
        this.name = name;
    }

    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }

    @Override
    public V put(String key, V value) {
        if (containsKey(key)) {
            throw new RuntimeException("已经存在的key, keyName = " + key);
        }

        if (key.contains(".")) {
            final String shortName = getShortName(key);
            if (containsKey(shortName)) {
                // question 这边有个问题， 为什么没有抛出ClassCastException。
                V ambiguity = (V) new Ambiguity("存在的shortName");
                super.put(shortName, ambiguity);
            } else {
                super.put(shortName, value);
            }
        }

        return super.put(key, value);
    }

    @Override
    public V get(Object key) {
        V value = super.get(key);
        if (value == null) {
            throw new RuntimeException("keyName = " + key + ", 没有获取到value.");
        }
        if (value instanceof Ambiguity) {
            throw new RuntimeException("重复的shortName");
        }
        return value;
    }

    static class Ambiguity {
        private String name;

        public Ambiguity(String name) {
            this.name = name;
        }

        public String getName() {
            return name;
        }
    }
}

ps:运行时也没报错。

Answer 1

类型擦除为Object，强转为Object不会报错。

Answer 2

编译时只会有警告，不会报错的。Java Collections Framework里其实到处是这样的强转。但运行时却会报错，如果V不是Ambiguity或者它的父类的话。