Comparable和Comparator介面的使用
一、Comparable介面，需要某一個類實現該介面，介面中複寫comparaTo（<T> o）方法，自己寫比較規則，示例程式碼如下
Person類，實現了Comparable介面，複寫了comparaTo方法
1 package cn.gao.day1019; 2 3 public class Person implements Comparable<Person> { 4 private String name; 5 private int age; 6 private double weight; 7 privatedouble height; 8 9 public Person() { 10 } 11 12 public Person(String name, int age, double weight, double height) { 13 this.name = name; 14 this.age = age; 15 this.weight = weight; 16 this.height = height; 17 } 18 19 public String getName() {20 return name; 21 } 22 23 public void setName(String name) { 24 this.name = name; 25 } 26 27 public int getAge() { 28 return age; 29 } 30 31 public void setAge(int age) { 32 this.age = age; 33 } 34 35 public double getWeight() { 36 returnweight; 37 } 38 39 public void setWeight(double weight) { 40 this.weight = weight; 41 } 42 43 public double getHeight() { 44 return height; 45 } 46 47 public void setHeight(double height) { 48 this.height = height; 49 } 50 51 @Override 52 public String toString() { 53 return "Person{" + 54 "name='" + name + '\'' + 55 ", age=" + age + 56 ", weight=" + weight + 57 ", height=" + height + 58 '}'; 59 } 60 61 @Override 62 public int compareTo(Person o) { 63 if(this.age<o.age){ 64 return -1; 65 } 66 else if (this.age>o.age){ 67 return 1; 68 } 69 return 0; 70 } 71 }
在測試類中，如果要排序該型別的陣列，可以直接呼叫Arrays.sort()方法，即可實現按自己寫的規則排序。
1 package cn.gao.day1019; 2 3 import java.util.Arrays; 4 5 public class PersonDemo1 { 6 public static void main(String[] args) { 7 Person[] per = {new Person("zhangsan",20,75.5,165.5), 8 new Person("lisi",25,88.5,193.4), 9 new Person("wangwu",18,60.5,175.7), 10 new Person("zhaoliu",23,72.4,181.2), 11 new Person("chenqi",16,53.5,162.5)}; 12 Arrays.sort(per); 13 for (Person person : per) { 14 System.out.println(person); 15 } 16 } 17 }
列印結果如下：可以看到按照comparaTo()中的櫃子，按照年齡的升序進行了排列。
Person{name='chenqi', age=16, weight=53.5, height=162.5}
Person{name='wangwu', age=18, weight=60.5, height=175.7}
Person{name='zhangsan', age=20, weight=75.5, height=165.5}
Person{name='zhaoliu', age=23, weight=72.4, height=181.2}
Person{name='lisi', age=25, weight=88.5, height=193.4}
二、Comparator需要根據不同屬性的比較，分別寫不同的實現類。
Person類不變，還是上面的原樣，按Age比較的類如下
1 package cn.gao.day1019; 2 3 import java.util.Comparator; 4 5 /** 6 * 實現按age排序的類 7 */ 8 public class PersonSortByAge implements Comparator<Person> { 9 @Override 10 public int compare(Person o1, Person o2) { 11 if (o1.getAge() < o2.getAge()) { 12 return -1; 13 } else if (o1.getAge() > o2.getAge()) { 14 return 1; 15 } 16 return 0; 17 } 18 }
按Height比較的類如下
1 package cn.gao.day1019; 2 3 import java.util.Comparator; 4 5 /** 6 * 實現按height比較的類 7 */ 8 public class PersonSortByHeight implements Comparator<Person> { 9 @Override 10 public int compare(Person o1, Person o2) { 11 if (o1.getHeight() < o2.getHeight()) { 12 return -1; 13 } else if (o1.getHeight() > o2.getHeight()) { 14 return 1; 15 } 16 return 0; 17 } 18 }
按Weight比較的類如下
1 package cn.gao.day1019; 2 3 import java.util.Comparator; 4 5 /** 6 * 實現按weight比較的類 7 */ 8 public class PersonSortByWeight implements Comparator<Person> { 9 @Override 10 public int compare(Person o1, Person o2) { 11 if (o1.getWeight() < o2.getWeight()) { 12 return -1; 13 } else if (o1.getWeight() > o2.getWeight()) { 14 return 1; 15 } 16 return 0; 17 } 18 }
測試類如下
1 package cn.gao.day1019; 2 3 import java.util.Arrays; 4 import java.util.Comparator; 5 6 public class PersonDemo2 { 7 public static void main(String[] args) { 8 Person[] per = {new Person("zhangsan", 20, 75.5, 165.5), 9 new Person("lisi", 25, 88.5, 193.4), 10 new Person("wangwu", 18, 60.5, 175.7), 11 new Person("zhaoliu", 23, 72.4, 181.2), 12 new Person("chenqi", 16, 53.5, 162.5)}; 13 System.out.println("按age排序"); 14 Arrays.sort(per, new PersonSortByAge()); 15 for (Person person : per) { 16 System.out.println(person); 17 } 18 System.out.println("按height排序"); 19 Arrays.sort(per, new PersonSortByHeight()); 20 for (Person person : per) { 21 System.out.println(person); 22 } 23 System.out.println("按weight排序"); 24 Arrays.sort(per, new PersonSortByWeight()); 25 for (Person person : per) { 26 System.out.println(person); 27 } 28 } 29 }
執行結果如下：
按age排序
Person{name='chenqi', age=16, weight=53.5, height=162.5}
Person{name='wangwu', age=18, weight=60.5, height=175.7}
Person{name='zhangsan', age=20, weight=75.5, height=165.5}
Person{name='zhaoliu', age=23, weight=72.4, height=181.2}
Person{name='lisi', age=25, weight=88.5, height=193.4}
按height排序
Person{name='chenqi', age=16, weight=53.5, height=162.5}
Person{name='zhangsan', age=20, weight=75.5, height=165.5}
Person{name='wangwu', age=18, weight=60.5, height=175.7}
Person{name='zhaoliu', age=23, weight=72.4, height=181.2}
Person{name='lisi', age=25, weight=88.5, height=193.4}
按weight排序
Person{name='chenqi', age=16, weight=53.5, height=162.5}
Person{name='wangwu', age=18, weight=60.5, height=175.7}
Person{name='zhaoliu', age=23, weight=72.4, height=181.2}
Person{name='zhangsan', age=20, weight=75.5, height=165.5}
Person{name='lisi', age=25, weight=88.5, height=193.4}
可以看出，結果已經分別按age、height、weight進行了排序
總結：Comparable介面，實現該介面後，需要實現介面中的comparaTo方法，自身實現了排序，就可以和基本資料型別陣列一樣，使用Arrays.sort（）方法進行排序了，傳遞引數為要排序的陣列物件。只能定義一種比較規則，如果比較規則發生改變，那麼就需要改動comparaTo()方法內的內容。
Comparator介面，該介面是單獨的一個類去實現，即提前準備好不同引數的比較方法，有幾套方法，就提前寫接個比較的類，也可以後期擴充套件比較的類。排序時，也呼叫Arrays.sort()，但是傳遞的引數除了陣列物件外，還要傳遞一個比較器物件。
Comparable介面較為單一，如果比較的引數固定，不存在多種情況，那麼採用這種方法即可，只需要類裡面實現comparaTo()方法，呼叫時直接傳遞待排序陣列即可。
Comparable介面是預定義幾種排序的類，同時後期可以根據業務擴充套件更多的排序類，擴充套件性強，呼叫時除了待排序的方法，還要傳遞排序類物件。