029_排序

同java一样：

在为对象数组进行排序时，比较器的作用非常明显，首先来讲解Comparable接口。

让需要进行排序的对象实现Comparable接口，重写其中的compareTo(T o)方法

The implementation of this method should return the following values:
-    0 if this instance and objectToCompareTo are equal
-    > 0 if this instance is greater than objectToCompareTo
-    < 0 if this instance is less than objectToCompareTo

看例子，这是Comparable接口的示例实现。

global class Employee implements Comparable {
public Long id;
public String name;
public String phone;
// Constructor
public Employee(Long i, String n, String p) {
id = i;
name = n;
phone = p;
}
// Implement the compareTo() method
global Integer compareTo(Object compareTo) {
Employee compareToEmp = (Employee)compareTo;
if (id == compareToEmp.id) return 0;
if (id > compareToEmp.id) return 1;
return -1;
}
}

 测试代码：

List<Employee> empList = new List<Employee>();
empList.add(new Employee(101,'Joe Smith', '4155551212'));
empList.add(new Employee(101,'J. Smith', '4155551212'));
empList.add(new Employee(25,'Caragh Smith', '4155551000'));
empList.add(new Employee(105,'Mario Ruiz', '4155551099'));
// Sort using the custom compareTo() method
empList.sort();
// Write list contents to the debug log
System.debug(empList);
// Verify list sort order.
System.assertEquals('Caragh Smith', empList[0].Name);
System.assertEquals('Joe Smith', empList[1].Name);
System.assertEquals('J. Smith', empList[2].Name);
System.assertEquals('Mario Ruiz', empList[3].Name);