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最近写一个java UI，需要用到垂直流布局管理器，要求该管理器能够实现内部组件的宽度自适应。看了swing提供的5个布局管理器，尝试的实现效果都不理想，看来只能自己搞一个了，好在网上已有实现，其测试效果如下图：

图一 垂直流布局管理器实现效果

具体代码如下：

清单一：

import java.awt.Component;import java.awt.Container;import java.awt.Dimension;import java.awt.FlowLayout;import java.awt.Insets;import javax.swing.JButton;import javax.swing.JFrame;/** * VerticalFlowLayout is similar to FlowLayout except it lays out components * vertically. Extends FlowLayout because it mimics much of the behavior of the * FlowLayout class, except vertically. An additional feature is that you can * specify a fill to edge flag, which causes the VerticalFlowLayout manager to * resize all components to expand to the column width Warning: This causes * problems when the main panel has less space that it needs and it seems to * prohibit multi-column output. Additionally there is a vertical fill flag, * which fills the last component to the remaining height of the container. */public class VFlowLayout extends FlowLayout{	/**	 * 	 */	private static final long serialVersionUID = 1L;	/**	 * Specify alignment top.	 */	public static final int TOP = 0;	/**	 * Specify a middle alignment.	 */	public static final int MIDDLE = 1;	/**	 * Specify the alignment to be bottom.	 */	public static final int BOTTOM = 2;	int hgap;	int vgap;	boolean hfill;	boolean vfill;	public static void main(String[] args)	{		System.out.println("Just for test ...");		JFrame frame = new JFrame();		frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);		frame.setBounds(0, 0, 600, 600);		frame.setLayout(new VFlowLayout());				int i = 0;		frame.add(new JButton(String.valueOf(i++)));		frame.add(new JButton(String.valueOf(i++)));		frame.add(new JButton(String.valueOf(i++)));		frame.add(new JButton(String.valueOf(i++)));		frame.add(new JButton(String.valueOf(i++)));		frame.add(new JButton(String.valueOf(i++)));		frame.add(new JButton(String.valueOf(i++)));		frame.add(new JButton(String.valueOf(i++)));		frame.add(new JButton(String.valueOf(i++)));		frame.add(new JButton(String.valueOf(i++)));		frame.add(new JButton(String.valueOf(i++)));				frame.setVisible(true);	}		/**	 * Construct a new VerticalFlowLayout with a middle alignment, and the fill	 * to edge flag set.	 */	public VFlowLayout()	{		this(TOP, 5, 5, true, false);	}	/**	 * Construct a new VerticalFlowLayout with a middle alignment.	 * 	 * @param hfill	 *            the fill to edge flag	 * @param vfill	 *            the vertical fill in pixels.	 */	public VFlowLayout(boolean hfill, boolean vfill)	{		this(TOP, 5, 5, hfill, vfill);	}	/**	 * Construct a new VerticalFlowLayout with a middle alignment.	 * 	 * @param align	 *            the alignment value	 */	public VFlowLayout(int align)	{		this(align, 5, 5, true, false);	}	/**	 * Construct a new VerticalFlowLayout.	 * 	 * @param align	 *            the alignment value	 * @param hfill	 *            the horizontalfill in pixels.	 * @param vfill	 *            the vertical fill in pixels.	 */	public VFlowLayout(int align, boolean hfill, boolean vfill)	{		this(align, 5, 5, hfill, vfill);	}	/**	 * Construct a new VerticalFlowLayout.	 * 	 * @param align	 *            the alignment value	 * @param hgap	 *            the horizontal gap variable	 * @param vgap	 *            the vertical gap variable	 * @param hfill	 *            the fill to edge flag	 * @param vfill	 *            true if the panel should vertically fill.	 */	public VFlowLayout(int align, int hgap, int vgap, boolean hfill, boolean vfill)	{		setAlignment(align);		this.hgap = hgap;		this.vgap = vgap;		this.hfill = hfill;		this.vfill = vfill;	}	/**	 * Returns the preferred dimensions given the components in the target	 * container.	 * 	 * @param target	 *            the component to lay out	 */	public Dimension preferredLayoutSize(Container target)	{		Dimension tarsiz = new Dimension(0, 0);		for (int i = 0; i < target.getComponentCount(); i++)		{			Component m = target.getComponent(i);						if (m.isVisible())			{				Dimension d = m.getPreferredSize();				tarsiz.width = Math.max(tarsiz.width, d.width);								if (i > 0)				{					tarsiz.height += hgap;				}								tarsiz.height += d.height;			}		}				Insets insets = target.getInsets();		tarsiz.width += insets.left + insets.right + hgap * 2;		tarsiz.height += insets.top + insets.bottom + vgap * 2;				return tarsiz;	}	/**	 * Returns the minimum size needed to layout the target container.	 * 	 * @param target	 *            the component to lay out.	 * @return the minimum layout dimension.	 */	public Dimension minimumLayoutSize(Container target)	{		Dimension tarsiz = new Dimension(0, 0);		for (int i = 0; i < target.getComponentCount(); i++)		{			Component m = target.getComponent(i);						if (m.isVisible())			{				Dimension d = m.getMinimumSize();				tarsiz.width = Math.max(tarsiz.width, d.width);								if (i > 0) 				{					tarsiz.height += vgap;				}								tarsiz.height += d.height;			}		}				Insets insets = target.getInsets();		tarsiz.width += insets.left + insets.right + hgap * 2;		tarsiz.height += insets.top + insets.bottom + vgap * 2;				return tarsiz;	}	/**	 * Set true to fill vertically.	 * 	 * @param vfill	 *            true to fill vertically.	 */	public void setVerticalFill(boolean vfill)	{		this.vfill = vfill;	}	/**	 * Returns true if the layout vertically fills.	 * 	 * @return true if vertically fills the layout using the specified.	 */	public boolean getVerticalFill()	{		return vfill;	}	/**	 * Set to true to enable horizontally fill.	 * 	 * @param hfill	 *            true to fill horizontally.	 */	public void setHorizontalFill(boolean hfill)	{		this.hfill = hfill;	}	/**	 * Returns true if the layout horizontally fills.	 * 	 * @return true if horizontally fills.	 */	public boolean getHorizontalFill()	{		return hfill;	}	/**	 * places the components defined by first to last within the target	 * container using the bounds box defined.	 * 	 * @param target	 *            the container.	 * @param x	 *            the x coordinate of the area.	 * @param y	 *            the y coordinate of the area.	 * @param width	 *            the width of the area.	 * @param height	 *            the height of the area.	 * @param first	 *            the first component of the container to place.	 * @param last	 *            the last component of the container to place.	 */	private void placethem(Container target, int x, int y, int width, int height, int first, int last)	{		int align = getAlignment();				if (align == MIDDLE)		{			y += height / 2;		}				if (align == BOTTOM)		{			y += height;		}				for (int i = first; i < last; i++)		{			Component m = target.getComponent(i);			Dimension md = m.getSize();						if (m.isVisible())			{				int px = x + (width - md.width) / 2;				m.setLocation(px, y);				y += vgap + md.height;			}		}	}	/**	 * Lays out the container.	 * 	 * @param target	 *            the container to lay out.	 */	public void layoutContainer(Container target)	{		Insets insets = target.getInsets();		int maxheight = target.getSize().height	- (insets.top + insets.bottom + vgap * 2);		int maxwidth = target.getSize().width - (insets.left + insets.right + hgap * 2);		int numcomp = target.getComponentCount();		int x = insets.left + hgap, y = 0;		int colw = 0, start = 0;		for (int i = 0; i < numcomp; i++)		{			Component m = target.getComponent(i);						if (m.isVisible()) 			{				Dimension d = m.getPreferredSize();								// fit last component to remaining height				if ((this.vfill) && (i == (numcomp - 1))) 				{					d.height = Math.max((maxheight - y), m.getPreferredSize().height);				}				// fit component size to container width				if (this.hfill)				{					m.setSize(maxwidth, d.height);					d.width = maxwidth;				} 				else				{					m.setSize(d.width, d.height);				}				if (y + d.height > maxheight)				{					placethem(target, x, insets.top + vgap, colw, maxheight - y, start, i);					y = d.height;					x += hgap + colw;					colw = d.width;					start = i;				} 				else				{					if (y > 0)					{						y += vgap;					}										y += d.height;					colw = Math.max(colw, d.width);				}			}		}				placethem(target, x, insets.top + vgap, colw, maxheight - y, start,	numcomp);	}}

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