reverse:

        public static void stringReverser() {
		String strOld = "aaabbb";
		String strNew = new StringBuffer(a).reverse().toString();
		System.out.println(strNew);
	}

	public static String replace(String text, String repl, String with) {
		if ((text == null) || (repl == null) || (with == null)
				|| (repl.length() == 0) || (max == 0)) {
			return text;
		}

		StringBuffer buf = new StringBuffer(text.length());
		int start = 0;
		int end = 0;

		while ((end = text.indexOf(repl, start)) != -1) {
			buf.append(text.substring(start, end)).append(with);
			start = end + repl.length();
		}

		buf.append(text.substring(start));
		return buf.toString();
	}

二: size增长.当需要增长时,Vectory为原来默认的一倍

 private void ensureCapacityHelper(int minCapacity) {
	int oldCapacity = elementData.length;
	if (minCapacity > oldCapacity) {
	    Object[] oldData = elementData;
	    int newCapacity = (capacityIncrement > 0) ?
		(oldCapacity + capacityIncrement) : (oldCapacity * 2);
    	    if (newCapacity < minCapacity) {
		newCapacity = minCapacity;
	    }
            elementData = Arrays.copyOf(elementData, newCapacity);
	}
    }

   public void ensureCapacity(int minCapacity) {
	modCount++;
	int oldCapacity = elementData.length;
	if (minCapacity > oldCapacity) {
	    Object oldData[] = elementData;
	    int newCapacity = (oldCapacity * 3)/2 + 1;
    	    if (newCapacity < minCapacity)
		newCapacity = minCapacity;
            // minCapacity is usually close to size, so this is a win:
            elementData = Arrays.copyOf(elementData, newCapacity);
	}
    }

二: HashMao 是可以用 null作为key和value的

3 char型能不能储存一个中文汉子?为什么?
答: 是能够储存一个中文汉字的,java使用的是unicode编码.一个char占16个字节,所以存储一个中文没问题哦.

4 多线程有几种实现方案？同步呢?
答: 有两种实现方案:
分别是继承 Runnable接口和Thread类.
同步也有两种实现方案 分别是 synchronized和notify