List<Integer>list=newArrayList<>(3);list.set(0,100);

• 在 Java 开发中，执行上述代码，出现如下错误信息

java.lang.IndexOutOfBoundsException: Index 0 out of bounds for length 0

问题原因

1. initialCapacity 是底层数组的大小，size 是列表中实际存储的元素个数

publicArrayList(intinitialCapacity){if(initialCapacity>0){this.elementData=newObject[initialCapacity];}elseif(initialCapacity==0){this.elementData=EMPTY_ELEMENTDATA;}else{thrownewIllegalArgumentException("Illegal Capacity: "+initialCapacity);}}

publicEset(intindex,Eelement){if(index>=size)thrownewIndexOutOfBoundsException(outOfBoundsMsg(index));EoldValue=(E)elementData[index];elementData[index]=element;returnoldValue;}

2. 调用 size 方法仍为 0

List<Integer>list=newArrayList<>(3);System.out.println(list.size());

# 输出结果 0

处理策略

• 初始化时填充 null 值

intinitialCapacity=3;List<Integer>list=newArrayList<>(initialCapacity);for(inti=0;i<initialCapacity;i++){list.add(null);}System.out.println(list.size());list.set(0,100);System.out.println(list.get(0));

# 输出结果 3 100