Consider learning Kotlin or Go instead if you are learning from scratch. Java consumes a lot of memory and likes to throw null pointer exceptions at you.

But the array is sorted, right? Please take a loook at Arrays.binarySearch in Java: https://docs.oracle.com/javase/8/docs/api/java/util/Arrays.html#binarySearch-int:A-int- Implementation: https://github.com/openjdk/jdk11/blob/master/src/java.base/share/classes/java/util/Arrays.java#L1828

JRE became part of the JDK package since version 11. https://stackoverflow.com/questions/55868821/when-jre-was-completely-discontinued-as-a-separate-offering So there's no way you can install "just JRE". I think mentioning JRE in the context of JDK can be misleading.