看HashMap 的源码，发现throw exception一个新用法

 1 public HashMap(int initialCapacity, float loadFactor) {
 2 　　　　　//此处对传入的初始容量进行校验，最大不能超过MAXIMUM_CAPACITY = 1<<30(230)
 3         if (initialCapacity < 0)
 4             throw new IllegalArgumentException("Illegal initial capacity: " +
 5                                                initialCapacity);
 6         if (initialCapacity > MAXIMUM_CAPACITY)
 7             initialCapacity = MAXIMUM_CAPACITY;
 8         if (loadFactor <= 0 || Float.isNaN(loadFactor))
 9             throw new IllegalArgumentException("Illegal load factor: " +
10                                                loadFactor);
11 
12         this.loadFactor = loadFactor;
13         threshold = initialCapacity;
14 　　　　　
15         init();//init方法在HashMap中没有实际实现，不过在其子类如 linkedHashMap中就会有对应实现
16     }

1  3         if (initialCapacity < 0)
2  4             throw new IllegalArgumentException("Illegal initial capacity: " +
3  5                                                initialCapacity);