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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);}@Overridepublic void addItem(AbstractComponent child) {}@Overridepublic void deleteItem(AbstractComponent child) {}@Overridepublic 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);}@Overridepublic void addItem(AbstractComponent child) {}@Overridepublic void deleteItem(AbstractComponent child) {}@Overridepublic 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();}});}
}