How to concatenate Strings in Java

In Java, there are several ways to concatenate strings. Here are some of the most common approaches:

Operator "+"

The "+" operator can be used to concatenate strings in Java. This is known as string concatenation.

String str1 = "Hello";
String str2 = " world!";
String result = str1 + str2;
System.out.println(result);

This approach is simple and can be used in expressions, but it can result in inefficiency if many concatenations are done in a loop due to the repeated creation of new "String" objects.

Method "concat()"

The "concat()" method of the "String" class can also be used to concatenate strings.

String str1 = "Hello";
String str2 = " world!";
String result = str1.concat(str2);
System.out.println(result);

The "concat()" method creates a new string that is the concatenation of the two original strings.

StringBuilder

For efficient concatenation operations in loops or when many concatenations are required, it is recommended to use the "StringBuilder" class, which is mutable and does not create new "String" objects with each concatenation.

StringBuilder builder = new StringBuilder();
builder.append("Hello");
builder.append(" world!");
String result = builder.toString();
System.out.println(result);

"StringBuilder" provides methods like "append()" to sequentially add strings and finally the "toString()" method to get the resulting string.

StringJoiner (Java 8)

Java 8 introduced the "StringJoiner" class, which offers a more declarative way of concatenating strings, especially when dealing with collections.

StringJoiner joiner = new StringJoiner(", ", "[", "]");
joiner.add("Apple");
joiner.add("Banana");
joiner.add("Orange");
String result = joiner.toString();
System.out.println(result);

"StringJoiner" allows you to specify a delimiter and prefix/suffix for the resulting string.

Choosing between these approaches depends on the specific context and requirements of your code. For simple operations, using the "+" operator or the "concat()" method may be sufficient. However, for more complex and efficient operations, especially in loops, considering using "StringBuilder" is generally more efficient.