• 这种模式适用于优化对带有递归特性数据结构的操作。例如链表、树这种数据结构，常见的有文件树、权限树等。
    • 它强调，既然在创建这种数据结构时，它就自带有递归的特性，那么对它操作的时候，也应该在保证效率的前提下，使用递归来简化屎一样的多个for循环。
    • 对于一棵树高为2的权限树，如果直接使用for循环，那么需要两层，如果树高为100呢？那废了。
    1.     public static void main(String[] args) {
    2.         Department leafDept1 = new Department("叶子部门1"); 
    3.         Department leafDept2 = new Department("叶子部门2");
    4.         Department leafDept3 = new Department("叶子部门3"); 
    6.         Department subDept1 = new Department("子部门1");
    7.         subDept1.getChildren().add(leafDept1);
    8.         subDept1.getChildren().add(leafDept2);
    10.         Department subDept2 = new Department("子部门2"); 
    11.         subDept2.getChildren().add(leafDept3);
    13.         Department parentDept = new Department("父部门");
    14.         parentDept.getChildren().add(subDept1);
    15.         parentDept.getChildren().add(subDept2);
    17.         for(Department subDept : parentDept.getChildren()) {
    18.             if(subDept.getChildren().size() > 0) {
    19.                 for(Department leafDept : subDept.getChildren()) {
    20.                     leafDept.remove();
    21.                 }
    22.             }
    23.             subDept.remove();
    24.         }
    25.         parentDept.remove();
    27.         // 问题：对层级数据的操作，很恶心，很不方便，需要手工编写大量的屎一样的代码
    28.         // 平时，屎一样代码的典型特征，四五个，六七个，for if else，嵌套，嵌套的非常深，1年后，团队里没人看得懂你写的代码
    29.     }
    31.     @Data
    32.     public static class Department {
    34.         private String name;
    35.         private List<Department> children = new ArrayList<Department>();
    37.         public Department(String name) {
    38.             super();
    39.             this.name = name;
    40.         }
    41.         public void remove() {
    42.             System.out.println("删除部门【" + name + "】");  
    43.         }
    45.     }
    • 使用组合模式优化后，将删除部门的功能使用递归实现。
    1. public static void main(String[] args) {
    2.         Department leafDept1 = new Department("叶子部门1"); 
    3.         Department leafDept2 = new Department("叶子部门2");
    4.         Department leafDept3 = new Department("叶子部门3"); 
    6.         Department subDept1 = new Department("子部门1");
    7.         subDept1.getChildren().add(leafDept1);
    8.         subDept1.getChildren().add(leafDept2);
    10.         Department subDept2 = new Department("子部门2"); 
    11.         subDept2.getChildren().add(leafDept3);
    13.         Department parentDept = new Department("父部门");
    14.         parentDept.getChildren().add(subDept1);
    15.         parentDept.getChildren().add(subDept2);
    17.         parentDept.remove();
    18.     }
    20.     @Data
    21.     public static class Department {
    23.         private String name;
    24.         private List<Department> children = new ArrayList<Department>();
    26.         public Department(String name) {
    27.             super();
    28.             this.name = name;
    29.         }
    30.         //这是重点
    31.         public void remove() {
    32.             if(children.size() > 0) {
    33.                 for(Department child : children) {
    34.                     child.remove();
    35.                 }
    36.             }
    37.             System.out.println("删除部门【" + name + "】");  
    38.         }
    40.     }