```java
import java.awt.Color;
import java.awt.image.BufferedImage;
import javax.swing.;
import java.util.;
import java.awt.*;
import java.io.File;
import java.io.IOException;
import javax.imageio.ImageIO;

public class DepthMapVisualizer {

public static void visualizeDepthMap(double[][] depthMap) {
    int width = depthMap[0].length;
    int height = depthMap.length;

    BufferedImage image = new BufferedImage(width, height, BufferedImage.TYPE_INT_RGB);

    // normalize depth map values to range [0, 255]
    double maxDepth = Double.MIN_VALUE;
    double minDepth = Double.MAX_VALUE;
    for (int i = 0; i < height; i++) {
        for (int j = 0; j < width; j++) {
            maxDepth = Math.max(maxDepth, depthMap[i][j]);
            minDepth = Math.min(minDepth, depthMap[i][j]);
        }
    }
    double depthRange = maxDepth - minDepth;
    for (int i = 0; i < height; i++) {
        for (int j = 0; j < width; j++) {
            double depth = (depthMap[i][j] - minDepth) / depthRange;
            Color color = getColor(depth);
            image.setRGB(j, i, color.getRGB());
        }
    }

    // create JFrame to display image
    JFrame frame = new JFrame("Depth Map");

    // create JPanel to display color bar
    JPanel colorBarPanel = new JPanel();
    colorBarPanel.setBackground(Color.white);
    JLabel colorBarLabel = new JLabel("Depth");
    colorBarPanel.add(colorBarLabel);

    // get color map from user
    Color[] colors = JColorChooser.showDialog(frame, "Choose a color map", 
                                              new Color[] {Color.BLUE, Color.GREEN, Color.YELLOW, Color.RED});
    int nColors = colors.length;
    for (int i = 0; i < nColors; i++) {
        JPanel colorPanel = new JPanel();
        colorPanel.setBackground(colors[i]);
        colorBarPanel.add(colorPanel);
        double depth = minDepth + (i * depthRange / (nColors - 1));
        JLabel depthLabel = new JLabel(String.format("%.2f", depth));
        colorBarPanel.add(depthLabel);
    }

    // create JLabel with image
    JLabel imageLabel = new JLabel(new ImageIcon(image));

    // create JPanel to hold image and color bar
    JPanel panel = new JPanel();
    panel.add(imageLabel);
    panel.add(colorBarPanel);

    // add panel to JFrame
    frame.getContentPane().add(panel);

    // show JFrame
    frame.pack();
    frame.setVisible(true);
}

private static Color getColor(double depth) {
    if (depth < 0.25) {
        return new Color(0, (int)(depth * 1020), 255);
    } else if (depth < 0.5) {
        return new Color(0, 255, 1020 - (int)(depth * 1020));
    } else if (depth < 0.75) {
        return new Color((int)(depth * 1020) - 255, 255, 0);
    } else {
        return new Color(255, 1020 - (int)(depth * 1020), 0);
    }
}
}
```
The above Java code converts the given Python code that creates a depth map and visualizes it using a color map to a Java code that does the same thing. The new code uses BufferedImage and JFrame classes to display the depth map. It also includes a color bar to show which depth corresponds to which color, and the user can choose a color map using the JColorChooser class.

To represent the depth map using colors, the getColor() method takes a depth value between 0 and 1 as input and returns a corresponding color. The colors are chosen such that the depth values are mapped to the red-green-blue color space, with lower depth values colored blue and higher depth values colored red. The getColor() method uses a simple linear mapping to convert depth values to colors.
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