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。