When the component orientation is changed from LTR to RTL or the other way around, JSplitPane exchanges the left and right components. However, it does this by adding and removing components instead of swapping the leftComponent and rightComponent fields which results in leftComponent field is left as null.
This is because when JSplitPane calls `setLeftComponent(rightComponent)` it calls `JSplitPane.addImpl` which calls `super.addImpl` which [removes] https://github.com/openjdk/jdk/blob/f423e1d9ad37135abacb8deb2d2151e21768a23e/src/java.desktop/share/classes/java/awt/Container.java#L1118 the component from the JSplitPane as it calls `JSplitPane.remove` so the sequence is At start `leftComponent = Red, rightComponent = Green` before `super.addImpl` is called in `JSplitPane.addImpl` the `leftComponent = Green, rightComponent = Green` After super.addImpl is called, it calls [JSplitPane.remove] (https://github.com/openjdk/jdk/blob/f423e1d9ad37135abacb8deb2d2151e21768a23e/src/java.desktop/share/classes/javax/swing/JSplitPane.java#L918) where it sets leftComponent = null. so we have leftComponent = null, rightComponent = Green and then it calls [super.remove] (https://github.com/openjdk/jdk/blob/f423e1d9ad37135abacb8deb2d2151e21768a23e/src/java.desktop/share/classes/javax/swing/JSplitPane.java#L922) which calls `JSplitPane.remove(index)` and since index=1 because "Green" is 1 it removes rightComponent so we have now leftComponent = null, rightComponent = null so when we now call [setRightComponent](https://github.com/openjdk/jdk/blob/f423e1d9ad37135abacb8deb2d2151e21768a23e/src/java.desktop/share/classes/javax/swing/JSplitPane.java#L382) it sets rightComponent to Red but leftComponent is not set and is still null. So fix is to just swap the left and right component in setComponentOrientation call itself without using Container add/remove components ------------- Commit messages: - 8365886: JSplitPane loses track of the left component when the component orientation is changed Changes: https://git.openjdk.org/jdk/pull/26893/files Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=26893&range=00 Issue: https://bugs.openjdk.org/browse/JDK-8365886 Stats: 40 lines in 2 files changed: 34 ins; 0 del; 6 mod Patch: https://git.openjdk.org/jdk/pull/26893.diff Fetch: git fetch https://git.openjdk.org/jdk.git pull/26893/head:pull/26893 PR: https://git.openjdk.org/jdk/pull/26893
