java 写法推荐

1. for循环

         // 1
         for (int i = 0; i < list.size(); i++) {
            int item = list.get(i);
            System.out.println("这是第" + (i+1) + "个：值为：" + item);
        }

        // 2
        int j = 0;
        for (int i : list) {
            ++j;
            System.out.println("这是第" + j + "个：值为：" + i);
        }

推荐写法2

2. HashMap遍历

    Map<String,String> map=new HashMap<String,String>();
        map.put("1", "value1");
        map.put("2", "value2");
        map.put("3", "value3");
        map.put("4", "value4");
     //第三种：推荐，尤其是容量大时
        System.out.println("\n通过Map.entrySet遍历key和value");
        for(Map.Entry<String, String> entry: map.entrySet())
        {
         System.out.println("Key: "+ entry.getKey()+ " Value: "+entry.getValue());
        }

3. 使用log4j的时候如何输出printStackTrace()的堆栈信息

log.error(e.getMessage(),e)

4. String拼接

StringBuilder tmpStr= new StringBuilder();
tmpStr.append(tmpStr1).append(tmpStr2).append(tmpStr3);
String aimStr = tmpStr.toString();