List轉換成String字串思路分析：
1.List轉化成String[],再通過String[]陣列遍歷拼接成String字串;
2.List轉化成String存到StringBuffer中,再通過StringButter中的append()方法拼接成String字串;
注意：StringBuffer字串變數、StringBuilder字串變數在方式二和方式三種可以把StringBuffer換成StringBuilder

方式一：

/*
 * List轉換成String字串
 * 方式一：
 *     分析：List轉化成String[],再通過String[]陣列遍歷拼接成String字串
 *
 * List內容：[laoyi, laoer, laosan]
 * 結果：laoyi,laoer,laosan
 * */
@SuppressWarnings({ "rawtypes", "unchecked", "unused" })
@Test
public void listToString01(){
    List list = new ArrayList();
    list.add("laoyi");
    list.add("laoer");
    list.add("laosan");

    System.out.println("List陣列："+list);
    if(list == null && list.size() == 0){
        System.out.println("list中的內容為空！");
    }else{

        String[] strArrStrings = new String[list.size()];
        String resultString = "";

        for(int i=0;i<=list.size()-1;i++){
            strArrStrings[i] = (String) list.get(i);
        }

        for(int j=0;j<=strArrStrings.length-1;j++){
            if(j < strArrStrings.length-1){
                resultString += strArrStrings[j] + ",";
            }else{
                resultString += strArrStrings[j];
            }
        }
        System.out.println("最後拼接的字串：" + resultString);
    }
}

/*
 * List轉換成String字串
 * 方式二：
 *     分析：List轉化成String存到StringBuilder中,再通過StringBuilder中的append()方法拼接成String字串
 * List內容：[laoyi, laoer, laosan]
 * 結果：laoyi,laoer,laosan
 * */
@SuppressWarnings({ "unused" })
@Test
public void listToString03(){
    List<String> list = new ArrayList<>();
    list.add("laoyi");
    list.add("laoer");
    list.add("laosan");
    if(null ==list && list.size()<=0){
        System.out.println("list內容為空！");
    }else{
        StringBuilder sb = new StringBuilder();
        String resultString = "";
        for(int i=0;i<list.size();i++){
            if(i<list.size()-1){
                sb.append(list.get(i));
                sb.append(",");
            }else{
                sb.append(list.get(i));
            }
        }
        resultString = sb.toString();
        System.out.println("最後拼接的字串結果：" + resultString);
    }
}

/*
 * List轉換成String字串
 * 方式三：
 *     分析：List轉化成String存到StringBuffer中,再通過StringButter中的append()方法拼接成String字串
 *
 * List內容：[laoyi, laoer, laosan]
 * 結果：laoyi,laoer,laosan
 * */
@SuppressWarnings({ "unused" })
@Test
public void listToString02(){
    List<String> list = new ArrayList<>();
    list.add("laoyi");
    list.add("laoer");
    list.add("laosan");

    if(null ==list && list.size()<=0){
        System.out.println("list內容為空！");
    }else{

        StringBuilder sb = new StringBuilder();
        String resultString = "";
        boolean flag = false;
        for(String str : list){
            if(flag){
                sb.append(",");
            }else{
                flag = true;
            }
            sb.append(str);
        }
        resultString = sb.toString();
        System.out.println("最後拼接的字串結果：" + resultString);
    }
}

本文來自部落格園，作者：我是一個小倉鼠，轉載請註明原文連結：https://www.cnblogs.com/yongyuankuaile/p/15420235.html