java設計模式-策略模式
public class Test { public static void main(String[] args) { int a[] = {9, 5, 3, 7, 1, 10}; DataSorter.sort(a); DataSorter.p(a); } }
DataSort:
package com.cy.dp.strategy; public class DataSorter {/** * 選擇排序法 * @param a public static void sort(int[] a) { int temp; for(int i=0; i<a.length; i++){ for(int j=i+1; j<a.length; j++){ if(a[i]>a[j]){ temp = a[i]; a[i] = a[j]; a[j] = temp; } } } }*/ /** * 冒泡排序法 * @param a */ public static void sort(int[] a) { int temp; for(int i=a.length; i>0; i--){ for(int j=0; j<i-1; j++){ if(a[j]>a[j+1]){ temp = a[j]; a[j] = a[j+1]; a[j+1] = temp; } } } } public static void p(int[] a) { for(int i=0; i<a.length; i++){ System.out.print(a[i] + " "); } System.out.println(); } }
但是上面有個問題:
sort方法裏面現在只能排序int類型的;
如果我想對於float類型進行排序,怎麽辦?--可以重載方法sort(float[] a);
如果想對於double類型的進行排序,怎麽辦?--再重載一個double參數的;
因為sort方法裏面a[j]和a[j+1]的int類型的,能直接比較,這還好辦,但是如果現在想DataSorter對貓、狗、Car、等等...進行排序,怎麽辦?
2.對所有對象的數組都能夠進行排序 定義比較接口Comparable://實現這個接口的類,表示是可以比較的 public interface Comparable { public int compareTo(Object o); }
DataSort可以排序任何類(該類實現Comparable接口),打印任何類;
寫完一次排序方法,再也不用改變了;
package com.cy.dp.strategy; public class DataSorter { /** * 冒泡排序法,排序任何類型,Object類型 * 假設Object[]裏面對象都實現了Comparable接口,都是可以比較大小的; * @param a */ public static void sort(Object[] a) { Object temp; for(int i=a.length; i>0; i--){ for(int j=0; j<i-1; j++){ Comparable o1 = (Comparable)a[j]; Comparable o2 = (Comparable)a[j+1]; if(o1.compareTo(o2) > 0){ temp = a[j]; a[j] = a[j+1]; a[j+1] = temp; } } } } public static void p(Object[] a) { for(int i=0; i<a.length; i++){ System.out.print(a[i] + " "); } System.out.println(); } }
Cat實現Compareble接口:
package com.cy.dp.strategy; public class Cat implements Comparable{ private int height; private int weight; public Cat(int height, int weight) { super(); this.height = height; this.weight = weight; } public int getHeight() { return height; } public void setHeight(int height) { this.height = height; } public int getWeight() { return weight; } public void setWeight(int weight) { this.weight = weight; } @Override public int compareTo(Object o) { if(o instanceof Cat){ Cat c = (Cat) o; if(this.getHeight()>c.getHeight()) return 1; else if(this.getHeight() < c.getHeight()) return -1; else return 0; } return -100; //簡單寫法,如果o不是cat,表示出錯;實際要拋異常 } @Override public String toString() { return height + "|" + weight; } }View Code
Dog實現Comparable接口:
package com.cy.dp.strategy; public class Dog implements Comparable{ private int food; public Dog(int food) { super(); this.food = food; } public int getFood() { return food; } public void setFood(int food) { this.food = food; } //對狗按照飯量大小進行排序 @Override public int compareTo(Object o) { Dog d = (Dog) o; if(this.food > d.getFood()) return 1; else if(this.food < d.getFood()) return -1; else return 0; } @Override public String toString() { return "Dog [food=" + food + "]"; } }View Code
測試:
public class Test { public static void main(String[] args) { Cat a[] = {new Cat(5,5), new Cat(3,3), new Cat(1,1)}; DataSorter.sort(a); DataSorter.p(a); Dog d[] = {new Dog(3), new Dog(1), new Dog(5), new Dog(4)}; DataSorter.sort(d); DataSorter.p(d); } }
輸出
1|1 3|3 5|5
Dog [food=1] Dog [food=3] Dog [food=4] Dog [food=5]
現在DataSort類可以對任何實現Comparable的類進行排序了,但是上面還是存在問題:
當前比較貓的大小的時候,只是根據貓的height,假如哪天要根據貓的weight、或者胡子的長度,或者別的來比較大小呢?怎麽辦?
也就是說現在Cat等實現的compareTo方法只能有一種實現,當還有其他不確定的實現時,這時候該怎麽設計?
3.實現Comparable接口的類,其compareTo方法,交給具體的比較策略,讓它去實現; 而不是說我自己固定寫死; Comparator:
//比較器 public interface Comparator { int compare(Object o1, Object o2); }
貓的高度比較器:
//兩只貓之間根據高度比較大小的 比較器 public class CatHeightComparator implements Comparator { @Override public int compare(Object o1, Object o2) { Cat c1 = (Cat) o1; Cat c2 = (Cat) o2; if(c1.getHeight()>c2.getHeight()) return 1; else if(c1.getHeight() < c2.getHeight()) return -1; else return 0; } }
貓的重量比較器:
//兩只貓之間根據重量比較大小的 比較器 public class CatWeightComparator implements Comparator { @Override public int compare(Object o1, Object o2) { Cat c1 = (Cat) o1; Cat c2 = (Cat) o2; if(c1.getWeight()>c2.getWeight()) return -1; else if(c1.getWeight() < c2.getWeight()) return 1; else return 0; } }
Cat類下面compareTo方法交給具體的比較器來實現:
package com.cy.dp.strategy; public class Cat implements Comparable{ private int height; private int weight; //默認是高度的比較器 //private Comparator comparator = new CatHeightComparator(); private Comparator comparator = new CatWeightComparator(); public Cat(int height, int weight) { super(); this.height = height; this.weight = weight; } public Comparator getComparator() { return comparator; } public void setComparator(Comparator comparator) { this.comparator = comparator; } public int getHeight() { return height; } public void setHeight(int height) { this.height = height; } public int getWeight() { return weight; } public void setWeight(int weight) { this.weight = weight; } @Override public int compareTo(Object o) { return comparator.compare(this, o); } @Override public String toString() { return height + "|" + weight; } }
測試程序:
public class Test { public static void main(String[] args) { Cat a[] = {new Cat(5,5), new Cat(3,3), new Cat(1,1)}; //Dog a[] = {new Dog(3), new Dog(1), new Dog(5), new Dog(4)}; DataSorter.sort(a); DataSorter.p(a); } }
輸出:5|5 3|3 1|1
4.看看JDK是怎麽做的:我們使用jdk裏面的Comparable接口、Comparator接口:
Cat:
package com.cy.dp.strategy; public class Cat implements java.lang.Comparable<Cat>{ private int height; private int weight; //默認是高度的比較器 private java.util.Comparator<Cat> comparator = new CatHeightComparator(); public Cat(int height, int weight) { super(); this.height = height; this.weight = weight; } public java.util.Comparator<Cat> getComparator() { return comparator; } public void setComparator(java.util.Comparator<Cat> comparator) { this.comparator = comparator; } public int getHeight() { return height; } public void setHeight(int height) { this.height = height; } public int getWeight() { return weight; } public void setWeight(int weight) { this.weight = weight; } @Override public int compareTo(Cat o) { return comparator.compare(this, o); } @Override public String toString() { return height + "|" + weight; } }
根據高度的比較器CatHeightComparator:
//兩只貓之間根據高度比較大小的 比較器 public class CatHeightComparator implements java.util.Comparator<Cat> { @Override public int compare(Cat c1, Cat c2) { if(c1.getHeight()>c2.getHeight()) return 1; else if(c1.getHeight() < c2.getHeight()) return -1; else return 0; } }
DataSort也改一下,就是使用java.lang.Comparable,其他不變:
package com.cy.dp.strategy; import java.lang.Comparable; public class DataSorter { /** * 冒泡排序法,排序任何類型,Object類型 * 假設Object[]裏面對象都實現了Comparable接口,都是可以比較大小的; * @param a */ public static void sort(Object[] a) { Object temp; for(int i=a.length; i>0; i--){ for(int j=0; j<i-1; j++){ Comparable o1 = (Comparable)a[j]; Comparable o2 = (Comparable)a[j+1]; if(o1.compareTo(o2) > 0){ temp = a[j]; a[j] = a[j+1]; a[j+1] = temp; } } } } public static void p(Object[] a) { for(int i=0; i<a.length; i++){ System.out.print(a[i] + " "); } System.out.println(); } }
測試代碼:
public class Test { public static void main(String[] args) { Cat a[] = {new Cat(5,5), new Cat(3,3), new Cat(1,1)}; //Dog a[] = {new Dog(3), new Dog(1), new Dog(5), new Dog(4)}; DataSorter.sort(a); DataSorter.p(a); } }
輸出:1|1 3|3 5|5
完美和JDK融合;基本模擬了JDK裏面的Comparable接口和Comparator接口;
5.而且其實不用自己寫DataSort,用Arrays就行了:
public static void main(String[] args) { Cat a[] = {new Cat(5,5), new Cat(3,3), new Cat(1,1)}; //Dog a[] = {new Dog(3), new Dog(1), new Dog(5), new Dog(4)}; //DataSorter.sort(a); java.util.Arrays.sort(a); //Arrays.sort(Object[] a) 註:a必須實現Comparable接口 DataSorter.p(a); }
也可以:
public static void main(String[] args) { Cat a[] = {new Cat(5,5), new Cat(3,3), new Cat(1,1)}; //Dog a[] = {new Dog(3), new Dog(1), new Dog(5), new Dog(4)}; //DataSorter.sort(a); //java.util.Arrays.sort(a); java.util.Arrays.sort(a, new java.util.Comparator<Cat>(){ @Override public int compare(Cat o1, Cat o2) { return o1.getHeight()>o2.getHeight()?1 :o1.getHeight()<o2.getHeight()?-1 :0; } }); DataSorter.p(a); }
小結:
策略模式就是說,當我進行比較大小的時候,我定義一個策略的比較器,然後由具體的比較策略來決定誰大誰小;
使用例子,比如:
1.封裝一下商場的打折策略;
周六打折,過年打折,兩種加在一塊就打折,等等。所以打折策略最好不要寫死它,因為將來可能有不能確定的各種各樣的打折策略;所以最好把打折策略定義成一個可以擴展的內容;這就是策略模式;
2.封裝一下坦克的發射炮彈的策略;
有的時候打一發,有的時候打多發,等等,具體由我發射炮彈的策略決定;
java設計模式-策略模式