StringBuild和StringBuffer区别

  @Override
    public synchronized StringBuffer append(String str) {
        toStringCache = null;
        super.append(str);
        return this;
    }

    @Override
public StringBuilder append(String str) {
    super.append(str);
    return this;
}

区别StringBuffer 方法全部采用 synchronized 修饰

 @Override
    public synchronized String toString() {
        if (toStringCache == null) {
            toStringCache = Arrays.copyOfRange(value, 0, count);
        }
        return new String(toStringCache, true);
    }

toStringCache = null; 为StringBuffer 专有，tostring缓存