Thursday, July 5, 2018

Applying New JDK 11 String Methods

In the posts "New Methods on Java String with JDK 11" and "String#repeat Coming to Java?", I discussed six new methods coming to the Java String with JDK 11. The available early access JDK 11 builds already include these new methods and I use one of those early access builds to demonstrate them in this post.

I am using OpenJDK JDK 11 Early Access Build 20 for compiling and running the examples shown in this post.

The six methods added to String for JDK 11 that are demonstrated in this post via the OpenJDK JDK 11 Early Access Build 20 are:

  • String.repeat(int)
  • String.lines()
  • String.strip()
  • String.stripLeading()
  • String.stripTrailing()
  • String.isBlank()

The source code for the examples demonstrated in this post is available on GitHub.


The String.repeat(int) method provides handy functionality that I've wished to see in Java since experiencing this functionality in Groovy. As its name suggests, this method repeats the String it is run against as many times as provided by the int parameter. I will likely use this method frequently in the future when generating simple demonstrations and use it for this post's examples. The next code listing demonstrates use of String.repeat(int) to easily generate header separators for the demonstration output.

Use of String.repeat(int)

 * Write provided {@code String} in header. Note that this
 * implementation uses {@code String.repeat(int)}.
 * @param headerText Title of header.
private static void writeHeader(final String headerText)
   final String headerSeparator = "=".repeat(headerText.length()+4);
   out.println("\n" + headerSeparator);
   out.println("= " + headerText + " =");

The writeHeader(String) method uses String.repeat(int) to easily generate "header separator" lines from the "=" character enough times to cover the provided headerText length plus 4 additional characters to allow for an extra "=" and extra space on each side of the "header text". The writeHeader(String) method is used by all the other demonstration examples in this post and so will be demonstrated via those examples.


The String.lines() method splits the String upon which it is called by its line terminators and returns a Stream of Strings as demarcated by those line terminators.

Use of String.lines()

 * Demonstrate method {@code String.lines()} added with JDK 11.
public static void demonstrateStringLines()
   final String originalString = prepareStringWithLineTerminators();
   final String stringWithoutLineSeparators
      = originalString.replaceAll("\\n", "\\\\n");
   writeHeader("String.lines() on '"  + stringWithoutLineSeparators  + "'");
   final Stream<String> strings = originalString.lines();

Sample output is shown in the next screen snapshot.

String.strip() / String.stripLeading() / String.stripTrailing()

The String.strip(), String.stripLeading(), and String.stripTrailing() methods trim white space [as determined by Character.isWhiteSpace()] off either the front, back, or both front and back of the targeted String.

Use of String.strip() / String.stripLeading() / String.stripTrailing()

 * Demonstrate method {@code String.strip()} added with JDK 11.
public static void demonstrateStringStrip()
   final String originalString = prepareStringSurroundedBySpaces();
   writeHeader("String.strip() on '" + originalString + "'");
   out.println("'" + originalString.strip() + "'");

 * Demonstrate method {@code String.stripLeading()} added with JDK 11.
public static void demonstrateStringStripLeading()
   final String originalString = prepareStringSurroundedBySpaces();
   writeHeader("String.stripLeading() on '" + originalString + "'");
   out.println("'" + originalString.stripLeading() + "'");

 * Demonstrate method {@code String.stripTrailing()} added with JDK 11.
public static void demonstrateStringStripTrailing()
   final String originalString = prepareStringSurroundedBySpaces();
   writeHeader("String.stripTrailing() on '" + originalString + "'");
   out.println("'" + originalString.stripTrailing() + "'");

When the above code is executed, the output looks like that shown in the next screen snapshot.


The String.isBlank() method indicates if the targeted String is empty or contains only white space characters as determined by Character.isWhitespace(int).

Use of String.isBlank()

 * Demonstrate method {@code String.isBlank()} added with JDK 11.
public static void demonstrateStringIsBlank()
   final String emptyString = "";
   out.println("Empty String -> " + emptyString.isBlank());
   final String onlyLineSeparator = System.getProperty("line.separator");
   out.println("Line Separator Only -> " + onlyLineSeparator.isBlank());
   final String tabOnly = "\t";
   out.println("Tab Only -> " + tabOnly.isBlank());
   final String spacesOnly = "   ";
   out.println("Spaces Only -> " + spacesOnly.isBlank());

An example of executing this code is shown in the next screen snapshot.

Some of the methods whose code is shown above call "helper" methods that can be seen on GitHub.

The methods added to JDK 11's String are small additions, but will make certain "presentation" tasks related to Java Strings easier than in the past and reduce the need for third-party libraries.


Brett Wooldridge said...


Unknown said...

String.repeat(int) will certainly make all those "how do I write my name 1,000 times in Java" questions that pop on on Quora a lot easier to answer. String.isBlank() might get confused with String.isEmpty(), but it will make things easier.

Unknown said...

Didn't get difference between String.trim() and String.strip()

Unknown said...

hmmm surely isBlank should be static since you can then go String.isblank(somesString) without null pointer problems.