[JAVA] How to connect the strings in the List separated by commas

About this article

There are times when the value returned from DAO is in the List and I want to concatenate the values and retrieve them. This time I will leave a memorandum about how to do it in such a case.

Note) If you use the second method as it is, a warning will appear at compile time, so correct it. Please use it.

For the code itself, refer to the link below. [Java] Make the string array a comma-separated string

To try it as it is ...

Issue the following command at the command prompt

cd ListTest.Directory with java
javac ListTest.java
java ListTest 

<--- Execution result ----------------------------> Type of first list class java.lang.String The contents of the first list. Comma connection: a, b Second list type class java.lang.String The contents of the second list. Comma connection: c, d <--------------------------------------->



import java.util.*;

public class ListTest{

	 *A program that tests how to write a List
	 * http://d.hatena.ne.jp/mtoyoshi/20080717/1216299220
	 * @Disable compile warnings in SuppressWarnings
     public static void main(String[] args){

     	/*The first one
     	List<String> lst = new ArrayList<String>();

     	StringBuilder builder = new StringBuilder();
     	//Type confirmation
     	System.out.println("Type of first list" + lst.get(0).getClass());
     	for(String str : lst) {

		String result = builder.substring(0, builder.length() - 1);
        System.out.println("The contents of the first list. Comma connection:" + result);

     	* List<String> lst2 = new ArrayList<String>();Otherwise you will get a compile-time warning
     	List lst2 = new ArrayList();

     	StringBuilder builder2 = new StringBuilder();
     	//Type confirmation
     	System.out.println("Second list type" + lst2.get(0).getClass());
		for (int i = 0; i < lst2.size(); i++) {                        
            String str2  = (String)lst2.get(i);

		String result2 = builder2.substring(0, builder2.length() - 1);
        System.out.println("The contents of the second list. Comma connection:" + result2);

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