In this article, we will discuss how to join all strings using delimiter specified in the String’s join() method

1. String’s join() method:

This String method joins all strings using specified delimiter
and finally returns a composed string (or say concatenated string with delimiter)
There are 2 variants or overloaded join() methods
Both methods if the elements specified is null, then null is added
Note: this is newly introduced in Java 1.8 version

1.1 Method Signature:

public static String join(CharSequence delimiter, CharSequence... elements);

public static String join(CharSequence delimiter, Iterable<? extends CharSequence> elements);

1.2 Parameters:

delimiter –> this is used to separate each elements (each strings)
elements –> elements which will be joined together using delimiter

1.3 Returns:

join() method	Returns
join(CharSequence delimiter, CharSequence… elements);	Returns all elements joined together with delimiter in between all strings (i.e.; new composed string)
join(CharSequence delimiter, Iterable<? extends CharSequence> elements);	Returns all elements present in collection object joined together with delimiter in between (i.e.; new composed string from List or Set)

1.4 Throws:

String’s join() method throws NullPointerException, if delimiter is NULL

2. Examples on String.join() method:

To join all String elements with specified delimiter
To join all String elements present inside Collection classes with specified delimiter
To join all String elements when null is present as one such element
To join all String elements when delimiter is null

2.1 To join all String elements with specified delimiter

Here, all Strings that need to be joined or composed or concatenated are passed/supplied as arguments to join() method
whereas, in the next example-2, all Strings that need to be joined are added to list/set first and then this collection object is passed/supplied as arguments to join() method

Method Signature:

public static String join(CharSequence delimiter, CharSequence... elements);

StringJoinMethodForVarargs.java

package in.bench.resources.string.methods;

public class StringJoinMethodForVarargs {

	public static void main(String[] args) {

		// Example-1 : message returned is:
		// "BenchResources.Net-is-a-Java-weblog"
		// hyphen (-) is a delimiter
		String strDescForMessage = String.join("-",
				"BenchResources.Net", "is", "a",
				"Java", "weblog");

		// print to console
		System.out.println("The returned string message is : "
				+ strDescForMessage);
		

		// Example-2 : message returned is:
		// "www.BenchResources.Net"
		// dot or period (.) is a delimiter
		String strDescForWebUrl = String.join(".", "www",
				"BenchResources", "Net");

		// print to console
		System.out.println("The returned string web url is : "
				+ strDescForWebUrl);
		

		// Example-3 : message returned is:
		// "30/07/2014"
		// forward slash (/) is a delimiter
		String strDescForDate = String.join("/",
				"30", "07", "2014");

		// print to console
		System.out.println("The returned string date is : "
				+ strDescForDate);
	}
}

Output:

The returned string message is : BenchResources.Net-is-a-Java-weblog
The returned string web url is : www.BenchResources.Net
The returned string date is : 30/07/2014

2.2 To join all String elements present inside Collection classes with specified delimiter

Here, all String values are added to List/Set Collection
finally this Collection object is passed/supplied to join() method as arguments

Method Signature:

public static String join(CharSequence delimiter, Iterable<? extends CharSequence> elements);

StringJoinMethodForCollection.java

package in.bench.resources.string.methods;

import java.util.ArrayList;
import java.util.LinkedHashSet;
import java.util.List;
import java.util.Set;

public class StringJoinMethodForCollection {

	public static void main(String[] args) {

		// create ArrayList for adding string elements
		List<String> strList = new ArrayList<>();

		// add elements to List
		strList.add("BenchResources.Net");
		strList.add("is");
		strList.add("a");
		strList.add("Java");
		strList.add("weblog");

		// Example-1 : message returned is:
		// "BenchResources.Net-is-a-Java-weblog"
		// converting List to String using hyphen (-)
		String strMessage = String.join(" ", strList);

		// print to console
		System.out.println("The returned string message is : "
				+ strMessage);
		

		// create LinkedHashSet for adding string elements
		Set<String> strSet = new LinkedHashSet<String>();

		// add elements to Set
		strSet.add("www");
		strSet.add("BenchResources");
		strSet.add("Net");

		// Example-2 : message returned is:
		// "www.BenchResources.Net"
		// converting Set to String using dot/period (.)
		String strWebUrl = String.join(".", strSet);

		// print to console
		System.out.println("The returned string web url is : "
				+ strWebUrl);
	}
}

Output:

The returned string message is : BenchResources.Net is a Java weblog
The returned string web url is : www.BenchResources.Net

2.3 To join all String elements when null is present as one such element

StringJoinMethodForNull.java

package in.bench.resources.string.methods;

public class StringJoinMethodForNull {

	public static void main(String[] args) {

		// Example-1 : message returned is:
		// "Java-has-null-element"
		// hyphen (-) is a delimiter
		String strDescForMessage = String.join("-",
				"Java", "has", null, "element");

		// print to console
		System.out.println("The returned string message "
				+ "with NULL is : " + strDescForMessage);
	}
}

Output:

The returned string message with NULL is : Java-has-null-element

2.4 To join all String elements when delimiter is null

StringJoinMethodForNullDelimiter.java

package in.bench.resources.override.tostring;

public class StringJoinMethodForNullDelimiter {

	public static void main(String[] args) {

		// Example-1 : NPE thrown
		// null as delimiter
		String strDescForMessage = String.join(null,
				"test", "this", "string");

		// print to console
		System.out.println("The returned string message "
				+ "with NULL is : " + strDescForMessage);
	}
}

Output:

Exception in thread "main" java.lang.NullPointerException
at java.util.Objects.requireNonNull(Unknown Source)
at java.lang.String.join(Unknown Source)
at in.bench.resources.override.tostring
.StringJoinMethodForNullDelimiter
.main(StringJoinMethodForNullDelimiter.java:9)

References:

Happy Coding !!
Happy Learning !!

BenchResources.Net

Java tutorial for beginners

Java – String join() method

1. String’s join() method:

1.1 Method Signature:

1.2 Parameters:

1.3 Returns:

1.4 Throws:

2. Examples on String.join() method:

2.1 To join all String elements with specified delimiter

Method Signature:

StringJoinMethodForVarargs.java

Output:

2.2 To join all String elements present inside Collection classes with specified delimiter

Method Signature:

StringJoinMethodForCollection.java

Output:

2.3 To join all String elements when null is present as one such element

StringJoinMethodForNull.java

Output:

2.4 To join all String elements when delimiter is null

StringJoinMethodForNullDelimiter.java

Output:

Related Articles:

References:

Related

1. String’s join() method:

1.1 Method Signature:

1.2 Parameters:

1.3 Returns:

1.4 Throws:

2. Examples on String.join() method:

2.1 To join all String elements with specified delimiter

Method Signature:

StringJoinMethodForVarargs.java

Output:

2.2 To join all String elements present inside Collection classes with specified delimiter

Method Signature:

StringJoinMethodForCollection.java

Output:

2.3 To join all String elements when null is present as one such element

StringJoinMethodForNull.java

Output:

2.4 To join all String elements when delimiter is null

StringJoinMethodForNullDelimiter.java

Output:

Related Articles:

References:

Related

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