What are the different ways to concatenate strings in Java?

In Java, there are several ways to concatenate strings.

1. You can concatenate two strings together directly using the “+” operator. For example:

String str1 = "Hello";
String str2 = "World";
String result = str1 + str2; // result为"HelloWorld"

1. Utilize the concat() method in String: The String class offers a concat() method that can be used to append a specified string to the end of the original string. For example:

String str1 = "Hello";
String str2 = "World";
String result = str1.concat(str2); // result为"HelloWorld"

1. Using the append() method of StringBuilder or StringBuffer: The StringBuilder and StringBuffer classes provide an append() method that can be used to add a specified string to the end of the current string object. For example:

StringBuilder sb = new StringBuilder();
sb.append("Hello");
sb.append("World");
String result = sb.toString(); // result为"HelloWorld"

It’s important to note that StringBuilder is not thread-safe, while StringBuffer is thread-safe. Therefore, it is recommended to use StringBuilder in single-threaded environments and StringBuffer in multi-threaded environments.

All these methods can be used for string concatenation, the specific method chosen depends on the specific needs and scenarios.