Go语言视频零基础入门到精通

javalearner · 发表于 2014-10-30 23:56:42

一、定义范型类

/**
@author Cay Horstmann
*/
public class Pair< T> //范型类，T是类型参数，T只能是类类型
{
public Pair() { first = null; second = null; }
public Pair(T first, T second) {
this.first = first; this.second = second;
}
public T getFirst() { return first; }
public T getSecond() { return second; }
public void setFirst(T newValue) { first = newValue; }
public void setSecond(T newValue) { second = newValue; }
private T first;
private T second;
}

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  二、测试一

public class PairTest1
{
public static void main(String[] args)
{
String[] words = { "Mary", "had", "a", "little", "lamb" };
Pair< String> mm = ArrayAlg.minmax(words);//字符串版本的范型
System.out.println("min = " + mm.getFirst());
System.out.println("max = " + mm.getSecond());
}
}
class ArrayAlg
{
/**
Gets the minimum and maximum of an array of strings.
@param a an array of strings
@return a pair with the min and max value, or null if a is
null or empty
*/
public static Pair< String> minmax(String[] a)
{
if (a == null || a.length == 0) return null;
String min = a[0];
String max = a[0];
for (int i = 1; i < a.length; i++)
{
if (min.compareTo(a[i]) > 0) min = a[i];
if (max.compareTo(a[i]) < 0) max = a[i];
}
return new Pair< String>(min, max);
}
}
结果：
C:java>java PairTest1
min = Mary
max = little
三、测试二
import java.util.*;
public class PairTest2
{
public static void main(String[] args)
{
GregorianCalendar[] birthdays =
{
new GregorianCalendar(1906, Calendar.DECEMBER, 9), // G. Hopper
new GregorianCalendar(1815, Calendar.DECEMBER, 10), // A. Lovelace
new GregorianCalendar(1903, Calendar.DECEMBER, 3), // J. von Neumann
new GregorianCalendar(1910, Calendar.JUNE, 22), // K. Zuse
};
Pair< GregorianCalendar> mm = ArrayAlg.minmax(birthdays);//日期版的范型
System.out.println("min = " + mm.getFirst().getTime());
System.out.println("max = " + mm.getSecond().getTime());
}
}
class ArrayAlg
{
/**
Gets the minimum and maximum of an array of objects of type T.
@param a an array of objects of type T
@return a pair with the min and max value, or null if a is
null or empty
*/
public static < T extends Comparable> Pair< T> minmax(T[] a) //范型方法，注意类型参数在方法的返回类型之前声明。
{
if (a == null || a.length == 0) return null;
T min = a[0];
T max = a[0];
for (int i = 1; i < a.length; i++)
{
if (min.compareTo(a[i]) > 0) min = a[i];
if (max.compareTo(a[i]) < 0) max = a[i];
}
return new Pair< T>(min, max);
}
}
运行结果：
C:java>java PairTest2
min = Sun Dec 10 00:00:00 CST 1815
max = Wed Jun 22 00:00:00 CST 1910
四、测试三
import java.util.*;
public class PairTest3
{
public static void main(String[] args)
{
Manager ceo = new Manager("Gus Greedy", 800000, 2003, 12, 15);
Manager cfo = new Manager("Sid Sneaky", 600000, 2003, 12, 15);
Pair< Manager> buddies = new Pair< Manager>(ceo, cfo);//管理人员版的范型
printBuddies(buddies);
ceo.setBonus(1000000);
cfo.setBonus(500000);
Manager[] managers = { ceo, cfo };
Pair< Employee> result = new Pair< Employee>();//雇员版的范型
minMaxBonus(managers, result);
System.out.println("first: " + result.getFirst().getName()
+ ", second: " + result.getSecond().getName());
maxMinBonus(managers, result);
System.out.println("first: " + result.getFirst().getName()
+ ", second: " + result.getSecond().getName());
}
public static void printBuddies(Pair< ? extends Employee> p)//指定上界，只有Employee或其子类才是可接受的参数
{
Employee first = p.getFirst();
Employee second = p.getSecond();
System.out.println(first.getName() + " and " + second.getName() + " are buddies.");
}
public static void minMaxBonus(Manager[] a,Pair< ? super Manager> result)//指定下界，只有Manager的超类才是可接受的参数
{
if (a == null || a.length == 0) return;
Manager min = a[0];
Manager max = a[0];
for (int i = 1; i < a.length; i++)
{
if (min.getBonus() > a[i].getBonus()) min = a[i];
if (max.getBonus() < a[i].getBonus()) max = a[i];
}
result.setFirst(min);
result.setSecond(max);
}
public static void maxMinBonus(Manager[] a, Pair< ? super Manager> result)//指定了下界
{
minMaxBonus(a, result);
PairAlg.swapHelper(result); // OK--swapHelper captures wildcard type
}
}
class PairAlg
{
public static boolean hasNulls(Pair< ?> p)//通配符参数"?"表示未知类型,Pair< ?>可以匹配任一Pair对象
{
return p.getFirst() == null || p.getSecond() == null;
}
public static void swap(Pair< ?> p) { swapHelper(p); }
public static < T> void swapHelper(Pair< T> p)
{
T t = p.getFirst();
p.setFirst(p.getSecond());
p.setSecond(t);
}
}
//雇员类
class Employee
{
public Employee(String n, double s, int year, int month, int day)
{
name = n;//姓名
salary = s;//薪水
GregorianCalendar calendar = new GregorianCalendar(year, month - 1, day);
hireDay = calendar.getTime();//受雇的日期
}
public String getName()
{
return name;
}
public double getSalary()
{
return salary;
}
public Date getHireDay()
{
return hireDay;
}
public void raiseSalary(double byPercent)
{
double raise = salary * byPercent / 100;
salary += raise;
}
private String name;
private double salary;
private Date hireDay;
}
//管理人员类
class Manager extends Employee
{
/**
@param n the employee"s name
@param s the salary
@param year the hire year
@param month the hire month
@param day the hire day
*/
public Manager(String n, double s, int year, int month, int day)
{
super(n, s, year, month, day);
bonus = 0;
}
public double getSalary()
{
double baseSalary = super.getSalary();
return baseSalary + bonus;
}
public void setBonus(double b)
{
bonus = b;
}
public double getBonus()
{
return bonus;
}
private double bonus;//奖金
}
运行结果：
C:java>java PairTest3
Gus Greedy and Sid Sneaky are buddies.
first: Sid Sneaky, second: Gus Greedy
first: Gus Greedy, second: Sid Sneaky

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源码下载：http://file.javaxxz.com/2014/10/30/235642656.zip

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[泛型学习]范型入门实例