Expression can be folded into Stream chain

Reports expressions with a repeating pattern that could be replaced with Stream API or a String.join() call.

Example:

  boolean allStartWith(String a, String b, String c, String d, String prefix) {
    return a.startsWith(prefix) && b.startsWith(prefix) && c.startsWith(prefix) && d.startsWith(prefix);
  }

After the quick-fix is applied:

  boolean foo(String a, String b, String c, String d, String prefix) {
    return Stream.of(a, b, c, d).allMatch(s -> s.startsWith(prefix));
  }

Example:

  String joinAll(String a, String b, String c, String d) {
    return a + "," + b + "," + c + "," + d;
  }

After the quick-fix is applied:

  String joinAll(String a, String b, String c, String d) {
    return String.join(",", a, b, c, d);
  }

Locating this inspection

By ID

Can be used to locate inspection in e.g. Qodana configuration files, where you can quickly enable or disable it, or adjust its settings.

FoldExpressionIntoStream

Via Settings dialog

Path to the inspection settings via IntelliJ Platform IDE Settings dialog, when you need to adjust inspection settings directly from your IDE.

This inspection depends on the Java feature 'Stream and Optional API', which is available since Java 8.

New in 2018.2

Suppressing Inspection

You can suppress this inspection by placing the following comment marker before the code fragment where you no longer want messages from this inspection to appear:

//noinspection FoldExpressionIntoStream

More detailed instructions as well as other ways and options that you have can be found in the product documentation:

IntelliJ IDEA 2025.2

Inspection Details
By default bundled with:	IntelliJ IDEA 2025.2, Qodana for JVM 2025.2,

Last modified: 18 September 2025