在Java中将 ArrayList 转换为逗号分隔的字符串
要将 ArrayList 转换为逗号分隔的字符串,这些是Java中可用的方法。
- 使用 StringBuilder 的 append() 方法
- 使用 toString() 方法
- 使用 Apache Commons StringUtils 类
- 使用流 API
- 使用 String 类的 join() 方法
方法一(使用StringBuilder的append()方法): Java中的StringBuilder表示一个可变的字符序列。在下面的示例中,我们使用了 StringBuilder 的 append() 方法。 append 方法用于在现有字符串的最后位置连接或添加一组新字符。
句法 :
public StringBuilder append(char a)
参数:该方法接受单个参数a ,它是要附加其字符串表示的 Char 值。
返回值:该方法在执行追加操作后返回一个字符串对象。
Java
// Java program to Convert ArrayList to Comma Separated
// String
import java.util.ArrayList;
public class Main {
public static void main(String[] args)
{
// Create an ArrayList
ArrayList geeklist
= new ArrayList();
// Add elements to ArrayList
geeklist.add("Hey");
geeklist.add("Geek");
geeklist.add("Welcome");
geeklist.add("to");
geeklist.add("geeksforgeeks");
geeklist.add("!");
StringBuilder str = new StringBuilder("");
// Traversing the ArrayList
for (String eachstring : geeklist) {
// Each element in ArrayList is appended
// followed by comma
str.append(eachstring).append(",");
}
// StringBuffer to String conversion
String commaseparatedlist = str.toString();
// By following condition you can remove the last
// comma
if (commaseparatedlist.length() > 0)
commaseparatedlist
= commaseparatedlist.substring(
0, commaseparatedlist.length() - 1);
System.out.println(commaseparatedlist);
}
}
Java
// Java program to Convert ArrayList to Comma Separated
// String in Java
import java.util.ArrayList;
public class Main {
public static void main(String[] args)
{
// Create an ArrayList
ArrayList geekcourses
= new ArrayList();
// Add elements to ArrayList
geekcourses.add("Data Structures");
geekcourses.add("Algorithms");
geekcourses.add("Operating System");
geekcourses.add("Computer Networks");
geekcourses.add("Machine Learning");
geekcourses.add("Databases");
/* toString method returns the output as [Data
Structure,Algorithms,...] In order to replace
'[', ']' and spaces with empty strings to get
comma separated values.*/
String commaseparatedlist = geekcourses.toString();
commaseparatedlist
= commaseparatedlist.replace("[", "")
.replace("]", "")
.replace(" ", "");
System.out.println(commaseparatedlist);
}
}
Java
// Java program to Convert ArrayList to Comma Separated
// String in Java
import java.util.ArrayList;
import org.apache.commons.collections4.CollectionUtils;
public class Main {
public static void main(String[] args)
{
// Create an ArrayList
ArrayList geekcourses
= new ArrayList();
// Add elements to ArrayList
geekcourses.add("Data Structures");
geekcourses.add("Algorithms");
geekcourses.add("Operating System");
geekcourses.add("Computer Networks");
geekcourses.add("Machine Learning");
geekcourses.add("Databases");
/*join method of StringUtils class is used
which returns a single string along with defined
separator in every iteration.*/
String commalist
= StringUtils.join(geekcourses, ",");
System.out.println(commalist);
}
}
Java
// Java program to Convert ArrayList to Comma Separated
// String in Java
import java.util.*;
import java.util.stream.Collectors;
public class Main {
public static void main(String[] args)
{
// Create ArrayList of String
ArrayList geeklist
= new ArrayList();
// add elements to ArrayList
geeklist.add("welcome");
geeklist.add("to");
geeklist.add("geeks");
geeklist.add("for");
geeklist.add("geeks");
// The collect method is used to return the result
// of the intermediate operations performed on the
// stream.
String str = geeklist.stream().collect(
Collectors.joining(","));
System.out.println(str);
}
}
Java
// Java program to Convert ArrayList to Comma Separated
// String in Java
import java.util.*;
import java.util.stream.Collectors;
public class Main {
public static void main(String[] args)
{
// Create ArrayList of String
ArrayList geeklist
= new ArrayList();
// add elements to ArrayList
geeklist.add("welcome");
geeklist.add("to");
geeklist.add("geeks");
geeklist.add("for");
geeklist.add("geeks");
// String.join() is used with a delimiter comma
// along with the list.
String str = String.join(",", geeklist);
System.out.println(str);
}
}
Hey,Geek,Welcome,to,geeksforgeeks,!
方法 2(使用 toString() 方法):toString()是一个内置方法,它以字符串格式返回给定的值。下面的代码使用 toString() 方法将 ArrayList 转换为 String。该方法返回应用了替换方法并替换指定字符(在本例中为括号和空格)的单个字符串。
句法:
arraylist.toString()
这里,arraylist 是 ArrayList 类的对象。
返回值:它返回数组列表的字符串表示
Java
// Java program to Convert ArrayList to Comma Separated
// String in Java
import java.util.ArrayList;
public class Main {
public static void main(String[] args)
{
// Create an ArrayList
ArrayList geekcourses
= new ArrayList();
// Add elements to ArrayList
geekcourses.add("Data Structures");
geekcourses.add("Algorithms");
geekcourses.add("Operating System");
geekcourses.add("Computer Networks");
geekcourses.add("Machine Learning");
geekcourses.add("Databases");
/* toString method returns the output as [Data
Structure,Algorithms,...] In order to replace
'[', ']' and spaces with empty strings to get
comma separated values.*/
String commaseparatedlist = geekcourses.toString();
commaseparatedlist
= commaseparatedlist.replace("[", "")
.replace("]", "")
.replace(" ", "");
System.out.println(commaseparatedlist);
}
}
DataStructures,Algorithms,OperatingSystem,ComputerNetworks,MachineLearning,Databases
方法 3(使用 Apache Commons StringUtils 类): Apache Commons 库有一个StringUtils类,为字符串提供实用函数。 join 方法用于将 ArrayList 转换为逗号分隔的字符串。
Java
// Java program to Convert ArrayList to Comma Separated
// String in Java
import java.util.ArrayList;
import org.apache.commons.collections4.CollectionUtils;
public class Main {
public static void main(String[] args)
{
// Create an ArrayList
ArrayList geekcourses
= new ArrayList();
// Add elements to ArrayList
geekcourses.add("Data Structures");
geekcourses.add("Algorithms");
geekcourses.add("Operating System");
geekcourses.add("Computer Networks");
geekcourses.add("Machine Learning");
geekcourses.add("Databases");
/*join method of StringUtils class is used
which returns a single string along with defined
separator in every iteration.*/
String commalist
= StringUtils.join(geekcourses, ",");
System.out.println(commalist);
}
}
输出
OutputDataStructures,Algorithms,OperatingSystem,ComputerNetworks,MachineLearning,Databases
方法四(Using Stream API): Stream API是Java 8中引入的,用于处理对象的集合。在Java中,Collectors 类的 join() 方法用于将字符或字符串数组的各种元素连接到单个字符串对象中。
Java
// Java program to Convert ArrayList to Comma Separated
// String in Java
import java.util.*;
import java.util.stream.Collectors;
public class Main {
public static void main(String[] args)
{
// Create ArrayList of String
ArrayList geeklist
= new ArrayList();
// add elements to ArrayList
geeklist.add("welcome");
geeklist.add("to");
geeklist.add("geeks");
geeklist.add("for");
geeklist.add("geeks");
// The collect method is used to return the result
// of the intermediate operations performed on the
// stream.
String str = geeklist.stream().collect(
Collectors.joining(","));
System.out.println(str);
}
}
welcome,to,geeks,for,geeks
方法 5(使用 String join() 方法:我们可以使用Java字符字符串转换为逗号分隔的 String提供的前缀并以提供的后缀结尾。String 类的 join() 方法可用于构造相同的内容。
Java
// Java program to Convert ArrayList to Comma Separated
// String in Java
import java.util.*;
import java.util.stream.Collectors;
public class Main {
public static void main(String[] args)
{
// Create ArrayList of String
ArrayList geeklist
= new ArrayList();
// add elements to ArrayList
geeklist.add("welcome");
geeklist.add("to");
geeklist.add("geeks");
geeklist.add("for");
geeklist.add("geeks");
// String.join() is used with a delimiter comma
// along with the list.
String str = String.join(",", geeklist);
System.out.println(str);
}
}
welcome,to,geeks,for,geeks