FlowLayout.java

// FlowLayout.java - Grid-based layout engine

/* Copyright (C) 1999, 2000, 2001, 2002  Free Software Foundation

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package java.awt;

import java.io.Serializable;

/** This class implements a flow-based layout.  Components are laid
 * out in order from left to right.  When a component cannot be placed
 * without horizontal clipping, a new row is started.  This class
 * supports horizontal and vertical gaps.  These are used for spacing
 * between components.
 *
 * @author Tom Tromey <tromey@redhat.com>
 * @author Aaron M. Renn (arenn@urbanophile.com)
 */
public class FlowLayout implements LayoutManager, Serializable
{
  /** Constant that specifies left alignment.  */
  public static final int LEFT = 0;
  /** Constant that specifies center alignment.  */
  public static final int CENTER = 1;
  /** Constant that specifies right alignment.  */
  public static final int RIGHT = 2;

  /** Constant that specifies alignment to leading edge of container's
   * orientation.  */
  public static final int LEADING = 3;
  /** Constant that specifies alignment to trailing edge of container's
   * orientation.  */
  public static final int TRAILING = 4;

  // Serialization constant
  private static final long serialVersionUID = -7262534875583282631L;

  /** Add a new component to the layout.  This particular implementation
   * does nothing.
   */
  public void addLayoutComponent (String name, Component comp)
  {
    // Nothing.
  }

  /**
   * Returns the current justification value for this object.
   *
   * @return The current justification value for this object.
   */
  public int getAlignment ()
  {
    return align;
  }

  /**
   * Returns the horizontal gap between components.
   *
   * @return The horizontal gap between components.
   */
  public int getHgap ()
  {
    return hgap;
  }

  /**
   * Returns the vertical gap between lines of components.
   *
   * @return The vertical gap between lines of components.
   */
  public int getVgap ()
  {
    return vgap;
  }

  /**
   * Initializes a new instance of <code>FlowLayout</code> with a center
   * justification and a default horizontal and vertical gap of 5.
   */
  public FlowLayout ()
  {
    this (CENTER, 5, 5);
  }

  /**
   * Initializes a new instance of <code>FlowLayout</code> with the specified
   * justification and a default horizontal and vertical gap of 5.
   *
   * @param align The justification setting, which should be one of the
   * contants in this class.
   */
  public FlowLayout (int align)
  {
    this (align, 5, 5);
  }

  /**
   * Initializes a new instance of <code>FlowLayout</code> with the specified
   * justification and gap values
   * @param align Alignment
   * @param hgap The horizontal gap
   * @param vgap The vertical gap
   * @exception IllegalArgumentException If either gap is negative
   */
  public FlowLayout (int align, int hgap, int vgap)
  {
    // Use methods to set fields so that we can have all the checking
    // in one place.
    setVgap (vgap);
    setHgap (hgap);
    setAlignment (align);
  }

  /** Lay out the container's components based on current settings.
   * @param parent The parent container
   */
  public void layoutContainer (Container parent)
  {
    synchronized (parent.getTreeLock ())
      {
	int num = parent.getComponentCount ();
	// This is more efficient than calling getComponents().
	Component[] comps = parent.component;

	Dimension d = parent.getSize ();
	Insets ins = parent.getInsets ();

	ComponentOrientation orient = parent.getComponentOrientation ();
	boolean left_to_right = orient.isLeftToRight ();

	int y = ins.top + vgap;
	int i = 0;
	while (i < num)
	  {
	    // Find the components which go in the current row.
	    int new_w = ins.left + hgap + ins.right;
	    int new_h = 0;
	    int j;
	    boolean found_one = false;
	    for (j = i; j < num; ++j)
	      {
		// Skip invisible items.
		if (! comps[j].visible)
		  continue;

		Dimension c = comps[j].getPreferredSize ();

		int next_w = new_w + hgap + c.width;
		if (next_w <= d.width || ! found_one)
		  {
		    new_w = next_w;
		    new_h = Math.max (new_h, c.height);
		    found_one = true;
		  }
		else
		  {
		    // Must start a new row, and we already found an item
		    break;
		  }
	      }

	    // Set the location of each component for this row.
	    int x;

	    int myalign = align;
	    if (align == LEADING)
	      myalign = left_to_right ? LEFT : RIGHT;
	    else if (align == TRAILING)
	      myalign = left_to_right ? RIGHT : LEFT;

	    if (myalign == LEFT)
	      x = ins.left + hgap;
	    else if (myalign == CENTER)
	      x = ins.left + (d.width - new_w) / 2 + hgap;
	    else
	      x = ins.left + (d.width - new_w) + hgap;

	    for (int k = i; k < j; ++k)
	      {
		if (comps[k].visible)
		  {
		    Dimension c = comps[k].getPreferredSize ();
		    comps[k].setBounds (x, y, c.width, new_h);
		    x += c.width + hgap;
		  }
	      }

	    // Advance to next row.
	    i = j;
	    y += new_h + vgap;
	  }
      }
  }

  /**
   * Returns the minimum layout size for the specified container using
   * this layout.
   * @param cont The parent container
   * @return The minimum layout size.
   */
  public Dimension minimumLayoutSize (Container cont)
  {
    return getSize (cont, true);
  }

  /**
   * Returns the preferred layout size for the specified container using
   * this layout.
   * @param cont The parent container
   * @return The preferred layout size.
   */
  public Dimension preferredLayoutSize (Container cont)
  {
    return getSize (cont, false);
  }

  /** Remove the indicated component from this layout manager.
   * This particular implementation does nothing.
   * @param comp The component to remove
   */
  public void removeLayoutComponent (Component comp)
  {
    // Nothing.
  }

  /**
   * Sets the justification value for this object to the specified value.
   *
   * @param align The new justification value for this object, which must
   * be one of the constants in this class.
   */
  public void setAlignment (int align)
  {
    if (align != LEFT && align != RIGHT && align != CENTER
	&& align != LEADING && align != TRAILING)
      throw new IllegalArgumentException ("invalid alignment: " + align);
    this.align = align;
  }

  /**
   * Sets the horizontal gap between components to the specified value.
   *
   * @param hgap The new horizontal gap between components.
   */
  public void setHgap (int hgap)
  {
    if (hgap < 0)
      throw new IllegalArgumentException ("horizontal gap must be nonnegative");
    this.hgap = hgap;
  }

  /**
   * Sets the vertical gap between lines of components to the specified value.
   *
   * @param vgap The new vertical gap.
   */
  public void setVgap (int vgap)
  {
    if (vgap < 0)
      throw new IllegalArgumentException ("vertical gap must be nonnegative");
    this.vgap = vgap;
  }

  /** Return String description of this object.
   * @return A string representation of this object.
   */
  public String toString ()
  {
    return ("[" + getClass ().getName () + ",hgap=" + hgap + ",vgap=" + vgap
	    + ",align=" + align + "]");
  }

  // This method is used to compute the various sizes.
  private Dimension getSize (Container parent, boolean is_min)
  {
    synchronized (parent.getTreeLock ())
      {
	int w, h, num = parent.getComponentCount ();
	// This is more efficient than calling getComponents().
	Component[] comps = parent.component;

	w = 0;
	h = 0;
	for (int i = 0; i < num; ++i)
	  {
	    if (! comps[i].visible)
	      continue;

	    // FIXME: can we just directly read the fields in Component?
	    // Or will that not work with subclassing?
	    Dimension d;

	    if (is_min)
	      d = comps[i].getMinimumSize ();
	    else
	      d = comps[i].getPreferredSize ();

	    w += d.width;
	    h = Math.max (d.height, h);
	  }

	Insets ins = parent.getInsets ();

	w += (num + 1) * hgap + ins.left + ins.right;
	h += 2 * vgap + ins.top + ins.bottom;

	return new Dimension (w, h);
      }
  }

  /**
   * @serial The justification alignment of the lines of components, which
   * will be one of the constants defined in this class.
   */
  private int align;

  /**
   * @serial The horizontal gap between components.
   */
  private int hgap;

  /**
   * @serial The vertical gap between lines of components.
   */
  private int vgap;
}