设计模式简述（十四）组合模式

描述

组合模式用于描述部分与整体的关系，将个体对象与组合对象的行为统一，便于维护整个数据集。

基本使用

所有节点方法一致

• 定义通用操作抽象组件

public abstract class AbstractComponent {
    private final String name;

    protected AbstractComponent(String name) {
        this.name = name;
    }

    public void description() {
        System.out.println("name: " + this.name);
    }

    public abstract void addItem(AbstractComponent child);

    public abstract void deleteItem(AbstractComponent child);

    public abstract List<AbstractComponent> getChildren();
}

• 定义树枝节点

public class ComplexComponent extends AbstractComponent {
    private final List<AbstractComponent> children = new ArrayList<>();

    protected ComplexComponent(String name) {
        super(name);
    }

    public void addItem(AbstractComponent child) {
        children.add(child);
    }

    public void deleteItem(AbstractComponent child) {
        children.remove(child);
    }

    public List<AbstractComponent> getChildren() {
        return children;
    }
}

• 定义叶子节点

public class LeafComponent extends AbstractComponent {
    protected LeafComponent(String name) {
        super(name);
    }

    @Override
    public void addItem(AbstractComponent child) {

    }

    @Override
    public void deleteItem(AbstractComponent child) {

    }

    @Override
    public List<AbstractComponent> getChildren() {
        return null;
    }
}

使用

由于所有节点操作一致，在使用中无需强转

public class Sample {
    public static void main(String[] args) {
        AbstractComponent root = new ComplexComponent("L1");
        AbstractComponent l2 = new ComplexComponent("L2");
        root.addItem(l2);
        AbstractComponent l2_1 = new ComplexComponent("L2_1");
        AbstractComponent l2_2 = new ComplexComponent("L2_2");
        l2.addItem(l2_1);
        l2.addItem(l2_2);
        AbstractComponent l2_1_1 = new ComplexComponent("L2_1_1");
        l2_1.addItem(l2_1_1);
        AbstractComponent l2_1_2 = new ComplexComponent("L2_1_2");
        l2_1.addItem(l2_1_2);
        printComponent(root);
    }

    private static void printComponent(AbstractComponent root) {
        root.description();
        root.getChildren().forEach(component -> {
            if (component instanceof ComplexComponent) {
                printComponent(component);
            } else {
                component.description();
            }
        });
    }
}

叶子无实现子节点

• 定义通用操作的抽象组件

public abstract class AbstractComponent {
    private final String name;

    protected AbstractComponent(String name) {
        this.name = name;
    }

    public void description() {
        System.out.println("name: " + this.name);
    }
}

• 定义树枝节点

public class ComplexComponent extends AbstractComponent {
    private final List<AbstractComponent> children = new ArrayList<>();

    protected ComplexComponent(String name) {
        super(name);
    }

    public void addItem(AbstractComponent child) {
        children.add(child);
    }

    public void deleteItem(AbstractComponent child) {
        children.remove(child);
    }

    public List<AbstractComponent> getChildren() {
        return children;
    }
}

• 定义叶子节点

public class LeafComponent extends AbstractComponent {
    protected LeafComponent(String name) {
        super(name);
    }
}

使用

public class Sample {
    public static void main(String[] args) {
        ComplexComponent root = new ComplexComponent("L1");
        ComplexComponent l2 = new ComplexComponent("L2");
        root.addItem(l2);
        ComplexComponent l2_1 = new ComplexComponent("L2_1");
        ComplexComponent l2_2 = new ComplexComponent("L2_2");
        l2.addItem(l2_1);
        l2.addItem(l2_2);
        ComplexComponent l2_1_1 = new ComplexComponent("L2_1_1");
        l2_1.addItem(l2_1_1);
        ComplexComponent l2_1_2 = new ComplexComponent("L2_1_2");
        l2_1.addItem(l2_1_2);
        printComponent(root);
    }

    private static void printComponent(ComplexComponent root) {
        root.description();
        root.getChildren().forEach(component -> {
            if (component instanceof ComplexComponent) {
                printComponent((ComplexComponent) component);
            } else {
                component.description();
            }
        });
    }
}

添加向上查询

在有的场景中，需要支持向上查询。
可以在通用抽象中定义一个上级节点，然后在父节点添加子节点同时为子节点关联父节点

• 定义通用抽象组件

public abstract class AbstractComponent {
    private final String name;
    /**
     * 新增了一个父级成员
     */
    private AbstractComponent parent;

    protected AbstractComponent(String name) {
        this.name = name;
    }

    public void description() {
        System.out.println("name: " + this.name + "  parent: " + (Objects.isNull(getParent()) ? "null" : getParent().getName()));
    }

    public abstract void addItem(AbstractComponent child);

    public abstract void deleteItem(AbstractComponent child);
    public abstract List<AbstractComponent> getChildren();

    public void setParent(AbstractComponent parent) {
        this.parent = parent;
    }

    public AbstractComponent getParent() {
        return parent;
    }

    public String getName() {
        return name;
    }
}

• 定义树枝节点

public class ComplexComponent extends AbstractComponent {
    private final List<AbstractComponent> children = new ArrayList<>();

    protected ComplexComponent(String name) {
        super(name);
    }

    /**
     * 在添加子节点时 同时设置子节点的父级节点
     * @param child
     */
    public void addItem(AbstractComponent child) {
        children.add(child);
        child.setParent(this);
    }

    /**
     * 在移除子节点时 同时清空子节点的父级节点
     * @param child
     */
    public void deleteItem(AbstractComponent child) {
        children.remove(child);
        child.setParent(null);
    }

    public List<AbstractComponent> getChildren() {
        return children;
    }
}

• 定义叶子节点（没变化）

public class LeafComponent extends AbstractComponent {
    protected LeafComponent(String name) {
        super(name);
    }

    @Override
    public void addItem(AbstractComponent child) {

    }

    @Override
    public void deleteItem(AbstractComponent child) {

    }

    @Override
    public List<AbstractComponent> getChildren() {
        return null;
    }
}

使用（没变化）

public class Sample {
    public static void main(String[] args) {
        AbstractComponent root = new ComplexComponent("L1");
        AbstractComponent l2 = new ComplexComponent("L2");
        root.addItem(l2);
        AbstractComponent l2_1 = new ComplexComponent("L2_1");
        AbstractComponent l2_2 = new ComplexComponent("L2_2");
        l2.addItem(l2_1);
        l2.addItem(l2_2);
        AbstractComponent l2_1_1 = new ComplexComponent("L2_1_1");
        l2_1.addItem(l2_1_1);
        AbstractComponent l2_1_2 = new ComplexComponent("L2_1_2");
        l2_1.addItem(l2_1_2);
        printComponent(root);
    }

    private static void printComponent(AbstractComponent root) {
        root.description();
        root.getChildren().forEach(component -> {
            if (component instanceof ComplexComponent) {
                printComponent(component);
            } else {
                component.description();
            }
        });
    }
}