Java 15 introduced text blocks as a standard feature.
Text blocks are multiline string literals written with three double quotes. They let developers include formatted SQL, JSON, HTML, source code, or other long text without filling ordinary string literals with escaped quotation marks, newline characters, and concatenation operators. The resulting value is still an ordinary java.lang.String.
The feature arrived earlier as a preview in Java 13 under JEP 355, then returned with refinements in Java 14 under JEP 368. Java 15, through JEP 378, finalized it as a permanent language feature, so programs could use it without enabling preview features. This history creates the common mix-up: Java 13 was the first release to preview text blocks, but Java 15 was the first release to make them standard.
Text blocks also have defined handling for incidental indentation and line terminators. The compiler removes incidental indentation according to the language rules and normalizes line endings, helping the same source produce predictable string content across platforms.