最近學習了下guava的使用，這裡簡單記錄下一些常用並且使用的工具類把。

看到table的使用時候真的是眼前一亮，之前的程式碼中寫過很多的Map<String,Map<String,String>> 這種格式的程式碼，這種閱讀起來非常的不友好，甚至都不知道map中的key到底是什麼還要聯絡上下文聯想才可以，而table型別的出現徹底解決掉了這個麻煩。

Table支援 row、column、value  我們把上面定義的map結構想象成一張資料表就可以了：

Table<R,C,V> == Map<R,Map<C,V>>

下面先讓我們來看一張資料表吧，結合資料表來編寫我們的程式碼：

下面是根據上面的表格寫的Demo

/*
         *  Company: IBM, Microsoft, TCS
         *  IBM         -> {101:Mahesh, 102:Ramesh, 103:Suresh}
         *  Microsoft     -> {101:Sohan, 102:Mohan, 103:Rohan }
         *  TCS         -> {101:Ram, 102: Shyam, 103: Sunil }
         *
         * */
        //create a table
        Table<String, String, String> employeeTable = HashBasedTable.create();

        //initialize the table with employee details
        employeeTable.put("IBM", "101","Mahesh");
        employeeTable.put("IBM", "102","Ramesh");
        employeeTable.put("IBM", "103","Suresh");

        employeeTable.put("Microsoft", "111","Sohan");
        employeeTable.put("Microsoft", "112","Mohan");
        employeeTable.put("Microsoft", "113","Rohan");

        employeeTable.put("TCS", "121","Ram");
        employeeTable.put("TCS", "102","Shyam");
        employeeTable.put("TCS", "123","Sunil");

        //所有行資料
        System.out.println(employeeTable.cellSet());
        //所有公司
        System.out.println(employeeTable.rowKeySet());
        //所有員工編號
        System.out.println(employeeTable.columnKeySet());
        //所有員工名稱
        System.out.println(employeeTable.values());
        //公司中的所有員工和員工編號
        System.out.println(employeeTable.rowMap());
        //員工編號對應的公司和員工名稱
        System.out.println(employeeTable.columnMap());
        //row+column對應的value
        System.out.println(employeeTable.get("IBM","101"));
        //IBM公司中所有資訊
        Map<String,String> ibmEmployees =  employeeTable.row("IBM");

        System.out.println("List of IBM Employees");
        for(Map.Entry<String, String> entry : ibmEmployees.entrySet()){
            System.out.println("Emp Id: " + entry.getKey() + ", Name: " + entry.getValue());
        }

        //table中所有的不重複的key
        Set<String> employers = employeeTable.rowKeySet();
        System.out.print("Employers: ");
        for(String employer: employers){
            System.out.print(employer + " ");
        }
        System.out.println();

        //得到員工編號為102的所有公司和姓名
        Map<String,String> EmployerMap =  employeeTable.column("102");
        for(Map.Entry<String, String> entry : EmployerMap.entrySet()){
            System.out.println("Employer: " + entry.getKey() + ", Name: " + entry.getValue());
        }

執行結果

[(IBM,101)=Mahesh, (IBM,102)=Ramesh, (IBM,103)=Suresh, (Microsoft,111)=Sohan, (Microsoft,112)=Mohan, (Microsoft,113)=Rohan, (TCS,121)=Ram, (TCS,102)=Shyam, (TCS,123)=Sunil]
[IBM, Microsoft, TCS]
[101, 102, 103, 111, 112, 113, 121, 123]
[Mahesh, Ramesh, Suresh, Sohan, Mohan, Rohan, Ram, Shyam, Sunil]
{IBM={101=Mahesh, 102=Ramesh, 103=Suresh}, Microsoft={111=Sohan, 112=Mohan, 113=Rohan}, TCS={121=Ram, 102=Shyam, 123=Sunil}}
{101={IBM=Mahesh}, 102={IBM=Ramesh, TCS=Shyam}, 103={IBM=Suresh}, 111={Microsoft=Sohan}, 112={Microsoft=Mohan}, 113={Microsoft=Rohan}, 121={TCS=Ram}, 123={TCS=Sunil}}
Mahesh
List of IBM Employees
Emp Id: 101, Name: Mahesh
Emp Id: 102, Name: Ramesh
Emp Id: 103, Name: Suresh
Employers: IBM Microsoft TCS 
Employer: IBM, Name: Ramesh
Employer: TCS, Name: Shyam