Resize panel when component moves to the next line in FlowLayout

 Code to adjust the height of the JPanel to the last component when the Resize event occurs

package test.swing;

import javax.swing.*;
import java.awt.*;
import java.awt.event.*;

// resize panel
public class MainTest {
    public static void main(String[] args) {
        MainUI mainUI = new MainUI();
        mainUI.setVisible(true);
    }
}

class MainUI extends JFrame {
    FlowLayout flowLayout = new FlowLayout(FlowLayout.LEFT, 0, 0);
    JPanel resizePane = new JPanel(flowLayout);
    JButton testBtn1 = new JButton("TEST 1");
    JButton testBtn2 = new JButton("TEST 2");
    JButton testBtn3 = new JButton("TEST 3");
    JButton testBtn4 = new JButton("TEST 4");
    JButton testBtn5 = new JButton("TEST 5");
    JComponent lastComponent = testBtn5;

    MainUI() {
        setPreferredSize(new Dimension(500, 300));
        setLayout(new BorderLayout());

        resizePane.setBackground(Color.BLUE);
        resizePane.addComponentListener(new ComponentAdapter() {
            Point prevPoint = null;

            @Override
            public void componentResized(ComponentEvent e) {
                super.componentResized(e);
                if (prevPoint == null || prevPoint.y != lastComponent.getLocation().y) {
                    System.out.println("lastComonent moved to " + lastComponent.getLocation());
                    resizePane.setPreferredSize(new Dimension(resizePane.getPreferredSize().width, lastComponent.getLocation().y + lastComponent.getHeight()));
                    resizePane.updateUI();
                }
                prevPoint = lastComponent.getLocation();
            }
        });

        resizePane.add(testBtn1);
        resizePane.add(testBtn2);
        resizePane.add(testBtn3);
        resizePane.add(testBtn4);
        resizePane.add(testBtn5);
        add(resizePane, BorderLayout.NORTH);

        JPanel pane = new JPanel();
        pane.add(new JLabel("TEST TEST"));
        add(pane, BorderLayout.CENTER);

        pack();
    }
}

RUN

Show tooltip when JComboBox key is pressed

 Code that shows tooltip when key occurs by key listener in JComboBox

package test.swing;

import javax.swing.*;
import java.awt.*;
import java.awt.event.KeyAdapter;
import java.awt.event.KeyEvent;
import java.awt.event.MouseEvent;

// key event tooltip
public class MainTest {
    public static void main(String[] args) {
        MainUI mainUI = new MainUI();
        mainUI.setVisible(true);
    }
}

class TestComboBox extends JComboBox {
    JTextField mTf = null;
    public TestComboBox() {
        super();
        mTf = (JTextField) editor.getEditorComponent();
        mTf.setToolTipText("TextField : ");
        mTf.addKeyListener(new KeyHandler());
    }

    class KeyHandler extends KeyAdapter {
        @Override
        public void keyReleased(KeyEvent e) {
            // set tooltip
            mTf.setToolTipText("TextField : " + mTf.getText());
            // show tooltip
            ToolTipManager.sharedInstance().mouseMoved(new MouseEvent(mTf, 0, 0, 0,0, 0, 0, false));
            super.keyReleased(e);
        }
    }
}

class MainUI extends JFrame {
    MainUI() {
        setPreferredSize(new Dimension(400, 300));
        setLayout(new FlowLayout());
        TestComboBox combo = new TestComboBox();
        combo.setToolTipText("ComboBox");
        combo.setEditable(true);
        add(combo);
        pack();
    }
}

java swing dynamic tooltip, multi-line tooltip

Implemented with getToolTipText method override

https://docs.oracle.com/javase/8/docs/api/javax/swing/JComponent.html#getToolTipText-java.awt.event.MouseEvent-

package test.swing;

import javax.swing.*;
import java.awt.*;
import java.awt.event.MouseEvent;

// dynamic tooltip
public class MainTest {
    public static void main(String[] args) {
        MainUI mainUI = new MainUI();
        mainUI.setVisible(true);
    }
}

class ToolTipButton extends JButton {
    boolean mIsNum = true;

    public ToolTipButton(String text) {
        super(text);
    }

    // 1. use setToolTipText
    @Override
    public String getToolTipText(MouseEvent event) {
        if (mIsNum) {
            setToolTipText("0123456789");
        }
        else {
            setToolTipText("ABCDEFG");
        }
        mIsNum = !mIsNum;
        return super.getToolTipText(event);
    }

    // 2. return text directly
    @Override
    public String getToolTipText(MouseEvent event) {
        String text = "";
        if (mIsNum) {
            text = "0123456789";
        }
        else {
            text = "ABCDEFG";
        }
        mIsNum = !mIsNum;
        return text;
    }
}

class MainUI extends JFrame {

    MainUI() {
        setPreferredSize(new Dimension(400, 300));
        setLayout(new FlowLayout());
        JButton button = new ToolTipButton("TEST");
        button.setToolTipText("");
        button.setPreferredSize(new Dimension(100, 100));
        add(button);
        pack();
    }
}

Multi-line tooltip

setToolTipText("<html>a<br>b</html>");

Registering a Java Swing KeyStroke

Close window when ESC is pressed

package test.swing;

import javax.swing.*;
import java.awt.*;
import java.awt.event.ActionEvent;
import java.awt.event.KeyEvent;
import java.awt.event.WindowEvent;

public class MainTest {
    public static void main(String[] args) {
        MainUI mainUI = new MainUI();
        mainUI.setVisible(true);
    }
}

class MainUI extends JFrame {
    MainUI() {
        setPreferredSize(new Dimension(400, 300));
        setLayout(new FlowLayout());
        JButton button = new JButton("TEST");
        button.setPreferredSize(new Dimension(100, 100));
        add(button);
        pack();

        KeyStroke escStroke = KeyStroke.getKeyStroke(KeyEvent.VK_ESCAPE, 0);
        String actionMapKey = getClass().getName() + ":WINDOW_CLOSING";
        Action closingAction = new AbstractAction() {
            public void actionPerformed(ActionEvent event) {
                MainUI.this.dispatchEvent(new WindowEvent(MainUI.this, WindowEvent.WINDOW_CLOSING));
            }
        };

        installKeyStroke(this, escStroke, actionMapKey, closingAction);
    }

    public void installKeyStroke(final RootPaneContainer container, final KeyStroke stroke, final String actionMapKey, final Action action) {
        JRootPane rootPane = container.getRootPane();
        rootPane.getInputMap(JComponent.WHEN_IN_FOCUSED_WINDOW).put(stroke, actionMapKey);
        rootPane.getActionMap().put(actionMapKey, action);
    }
}

Generate a key with the class name to be registered (to prevent duplication)

String actionMapKey = getClass().getName() + ":WINDOW_CLOSING";