组合在 Java 中的实现

组合是一种结构型设计模式，你可以使用它将对象组合成树状结构，并且能像使用独立对象一样使用它们。

对于绝大多数需要生成树状结构的问题来说，组合都是非常受欢迎的解决方案。组合最主要的功能是在整个树状结构上递归调用方法并对结果进行汇总。

在 Java 中使用模式

复杂度：⭐⭐

流行度：⭐⭐

使用实例： 组合模式在 Java 代码中很常见,常用于表示与图形打交道的用户界面组件或代码的层次结构。

下面是一些来自 Java 标准程序库中的组合示例：

java.awt.Container#add(Component) （几乎广泛存在于 Swing 组件中）
javax.faces.component.UIComponent#getChildren() （几乎广泛存在于 JSF UI 组件中）

识别方法： 组合可以通过将同一抽象或接口类型的实例放入树状结构的行为方法来轻松识别。

shapes

shapes/Shape.java: 通用形状接口

package refactoring_guru.composite.example.shapes;import java.awt.*;public interface Shape {int getX();int getY();int getWidth();int getHeight();void move(int x, int y);boolean isInsideBounds(int x, int y);void select();void unSelect();boolean isSelected();void paint(Graphics graphics);
}

shapes/BaseShape.java: 提供基本功能的抽象形状

package refactoring_guru.composite.example.shapes;import java.awt.*;abstract class BaseShape implements Shape {public int x;public int y;public Color color;private boolean selected = false;BaseShape(int x, int y, Color color) {this.x = x;this.y = y;this.color = color;}@Overridepublic int getX() {return x;}@Overridepublic int getY() {return y;}@Overridepublic int getWidth() {return 0;}@Overridepublic int getHeight() {return 0;}@Overridepublic void move(int x, int y) {this.x += x;this.y += y;}@Overridepublic boolean isInsideBounds(int x, int y) {return x > getX() && x < (getX() + getWidth()) &&y > getY() && y < (getY() + getHeight());}@Overridepublic void select() {selected = true;}@Overridepublic void unSelect() {selected = false;}@Overridepublic boolean isSelected() {return selected;}void enableSelectionStyle(Graphics graphics) {graphics.setColor(Color.LIGHT_GRAY);Graphics2D g2 = (Graphics2D) graphics;float dash1[] = {2.0f};g2.setStroke(new BasicStroke(1.0f,BasicStroke.CAP_BUTT,BasicStroke.JOIN_MITER,2.0f, dash1, 0.0f));}void disableSelectionStyle(Graphics graphics) {graphics.setColor(color);Graphics2D g2 = (Graphics2D) graphics;g2.setStroke(new BasicStroke());}@Overridepublic void paint(Graphics graphics) {if (isSelected()) {enableSelectionStyle(graphics);}else {disableSelectionStyle(graphics);}// ...}
}

shapes/Dot.java: 点

package refactoring_guru.composite.example.shapes;import java.awt.*;public class Dot extends BaseShape {private final int DOT_SIZE = 3;public Dot(int x, int y, Color color) {super(x, y, color);}@Overridepublic int getWidth() {return DOT_SIZE;}@Overridepublic int getHeight() {return DOT_SIZE;}@Overridepublic void paint(Graphics graphics) {super.paint(graphics);graphics.fillRect(x - 1, y - 1, getWidth(), getHeight());}
}

shapes/Circle.java: 圆形

package refactoring_guru.composite.example.shapes;import java.awt.*;public class Circle extends BaseShape {public int radius;public Circle(int x, int y, int radius, Color color) {super(x, y, color);this.radius = radius;}@Overridepublic int getWidth() {return radius * 2;}@Overridepublic int getHeight() {return radius * 2;}public void paint(Graphics graphics) {super.paint(graphics);graphics.drawOval(x, y, getWidth() - 1, getHeight() - 1);}
}

shapes/Rectangle.java: 三角形

package refactoring_guru.composite.example.shapes;import java.awt.*;public class Rectangle extends BaseShape {public int width;public int height;public Rectangle(int x, int y, int width, int height, Color color) {super(x, y, color);this.width = width;this.height = height;}@Overridepublic int getWidth() {return width;}@Overridepublic int getHeight() {return height;}@Overridepublic void paint(Graphics graphics) {super.paint(graphics);graphics.drawRect(x, y, getWidth() - 1, getHeight() - 1);}
}

shapes/CompoundShape.java: 由其他形状对象组成的复合形状

package refactoring_guru.composite.example.shapes;import java.awt.*;
import java.util.ArrayList;
import java.util.Arrays;
import java.util.List;public class CompoundShape extends BaseShape {protected List<Shape> children = new ArrayList<>();public CompoundShape(Shape... components) {super(0, 0, Color.BLACK);add(components);}public void add(Shape component) {children.add(component);}public void add(Shape... components) {children.addAll(Arrays.asList(components));}public void remove(Shape child) {children.remove(child);}public void remove(Shape... components) {children.removeAll(Arrays.asList(components));}public void clear() {children.clear();}@Overridepublic int getX() {if (children.size() == 0) {return 0;}int x = children.get(0).getX();for (Shape child : children) {if (child.getX() < x) {x = child.getX();}}return x;}@Overridepublic int getY() {if (children.size() == 0) {return 0;}int y = children.get(0).getY();for (Shape child : children) {if (child.getY() < y) {y = child.getY();}}return y;}@Overridepublic int getWidth() {int maxWidth = 0;int x = getX();for (Shape child : children) {int childsRelativeX = child.getX() - x;int childWidth = childsRelativeX + child.getWidth();if (childWidth > maxWidth) {maxWidth = childWidth;}}return maxWidth;}@Overridepublic int getHeight() {int maxHeight = 0;int y = getY();for (Shape child : children) {int childsRelativeY = child.getY() - y;int childHeight = childsRelativeY + child.getHeight();if (childHeight > maxHeight) {maxHeight = childHeight;}}return maxHeight;}@Overridepublic void move(int x, int y) {for (Shape child : children) {child.move(x, y);}}@Overridepublic boolean isInsideBounds(int x, int y) {for (Shape child : children) {if (child.isInsideBounds(x, y)) {return true;}}return false;}@Overridepublic void unSelect() {super.unSelect();for (Shape child : children) {child.unSelect();}}public boolean selectChildAt(int x, int y) {for (Shape child : children) {if (child.isInsideBounds(x, y)) {child.select();return true;}}return false;}@Overridepublic void paint(Graphics graphics) {if (isSelected()) {enableSelectionStyle(graphics);graphics.drawRect(getX() - 1, getY() - 1, getWidth() + 1, getHeight() + 1);disableSelectionStyle(graphics);}for (refactoring_guru.composite.example.shapes.Shape child : children) {child.paint(graphics);}}
}

editor

editor/ImageEditor.java: 形状编辑器

package refactoring_guru.composite.example.editor;import refactoring_guru.composite.example.shapes.CompoundShape;
import refactoring_guru.composite.example.shapes.Shape;import javax.swing.*;
import javax.swing.border.Border;
import java.awt.*;
import java.awt.event.MouseAdapter;
import java.awt.event.MouseEvent;public class ImageEditor {private EditorCanvas canvas;private CompoundShape allShapes = new CompoundShape();public ImageEditor() {canvas = new EditorCanvas();}public void loadShapes(Shape... shapes) {allShapes.clear();allShapes.add(shapes);canvas.refresh();}private class EditorCanvas extends Canvas {JFrame frame;private static final int PADDING = 10;EditorCanvas() {createFrame();refresh();addMouseListener(new MouseAdapter() {@Overridepublic void mousePressed(MouseEvent e) {allShapes.unSelect();allShapes.selectChildAt(e.getX(), e.getY());e.getComponent().repaint();}});}void createFrame() {frame = new JFrame();frame.setDefaultCloseOperation(WindowConstants.EXIT_ON_CLOSE);frame.setLocationRelativeTo(null);JPanel contentPanel = new JPanel();Border padding = BorderFactory.createEmptyBorder(PADDING, PADDING, PADDING, PADDING);contentPanel.setBorder(padding);frame.setContentPane(contentPanel);frame.add(this);frame.setVisible(true);frame.getContentPane().setBackground(Color.LIGHT_GRAY);}public int getWidth() {return allShapes.getX() + allShapes.getWidth() + PADDING;}public int getHeight() {return allShapes.getY() + allShapes.getHeight() + PADDING;}void refresh() {this.setSize(getWidth(), getHeight());frame.pack();}public void paint(Graphics graphics) {allShapes.paint(graphics);}}
}

Demo.java: 客户端代码

package refactoring_guru.composite.example;import refactoring_guru.composite.example.editor.ImageEditor;
import refactoring_guru.composite.example.shapes.Circle;
import refactoring_guru.composite.example.shapes.CompoundShape;
import refactoring_guru.composite.example.shapes.Dot;
import refactoring_guru.composite.example.shapes.Rectangle;import java.awt.*;public class Demo {public static void main(String[] args) {ImageEditor editor = new ImageEditor();editor.loadShapes(new Circle(10, 10, 10, Color.BLUE),new CompoundShape(new Circle(110, 110, 50, Color.RED),new Dot(160, 160, Color.RED)),new CompoundShape(new Rectangle(250, 250, 100, 100, Color.GREEN),new Dot(240, 240, Color.GREEN),new Dot(240, 360, Color.GREEN),new Dot(360, 360, Color.GREEN),new Dot(360, 240, Color.GREEN)));}
}

OutputDemo.png: 执行结果