java類如何按照某一屬性排序
阿新 • • 發佈：2018-12-05
1. 首先Person類，實現可按照屬性name或者age排序，Personl類如下：
2.首先看示例：利用Collections.sort方法實現對String,Integer...等等型別的排序class Person{ public String name; public int age; public Person(String name, int age) { super(); this.name = name; this.age = age; } public String getName() { return name; } public void setName(String name) { this.name = name; } public int getAge() { return age; } public void setAge(int age) { this.age = age; } @Override public String toString() { return "Person [name=" + name + ", age=" + age + "]"; } }
public class T1 { public static void main(String[] args) { List<String> list=new ArrayList<String>(); list.add("d"); list.add("f"); list.add("a"); sortString(list); System.out.println("==========="); List<Integer> list2=new ArrayList<Integer>(); list2.add(9); list2.add(5); list2.add(8); sortInteger(list2); } public static void sortString(List<String> list){ Collections.sort(list); for (String string : list) { System.out.println(string); } } public static void sortInteger(List<Integer> list){ Collections.sort(list); for (Integer integer : list) { System.out.println(integer); } } }
3.試試對Person類進行排序
public class T2 { public static void main(String[] args) { List<Person> list=new ArrayList<Person>(); Person p1=new Person("d",55); Person p2=new Person("c",18); Person p3=new Person("a",37); list.add(p1); list.add(p2); list.add(p3); sortPerson(list); } public static void sortPerson(List<Person> list){ Collections.sort(list);//編譯不通過!!!! } }
編譯器提示"The method sort(List<T>) in the type Collections is not applicable for the arguments (List<Person>)"
要想使用Collections.sort進行排序 該class 必須實現Comparable<Person>介面，並覆寫compareTo方法；現在對Person類進行改造：
class Person implements Comparable<Person>{
public String name;
public int age;
public Person(String name, int age) {
super();
this.name = name;
this.age = age;
}
public String getName() {
return name;
}
public void setName(String name) {
this.name = name;
}
public int getAge() {
return age;
}
public void setAge(int age) {
this.age = age;
}
@Override
public String toString() {
return "Person [name=" + name + ", age=" + age + "]";
}
@Override
public int compareTo(Person o) {
return this.getName().compareTo(o.getName());
}
}public class T2 {
public static void main(String[] args) {
List<Person> list=new ArrayList<Person>();
Person p1=new Person("d",55);
Person p2=new Person("c",18);
Person p3=new Person("a",37);
list.add(p1);
list.add(p2);
list.add(p3);
sortPerson(list);
}
public static void sortPerson(List<Person> list){
Collections.sort(list);//編譯通過；
for (Person person : list) {
System.out.println(person);
}
}
}
Person [name=a, age=37]
Person [name=c, age=18]
Person [name=d, age=55] 4.以上程式碼中實現了按照name屬性對List<Person>排序，如果想按照age屬性排序，需要修改>compareTo方法 如下：
@Override
public int compareTo(Person o) {
return new Integer(this.getAge()).compareTo(o.getAge());
}再次執行main方法測試結果如下：
Person [name=c, age=18]
Person [name=a, age=37]
Person [name=d, age=55]5.其他實現方式(1):Person類可以不實現Comparable<T>介面，而是呼叫public static <T> void sort(List<T> list, Comparator<? super T> c)方法實現排序。
public static void sortPerson(List<Person> list){
Collections.sort(list,new Comparator<Person>() {
@Override
public int compare(Person o1, Person o2) {
return o1.getName().compareTo (o2.getName());
}
});
for (Person person : list) {
System.out.println(person);
}
}6.其他實現方式(2):Person類可以不實現Comparable < T > 介面，而是通過自定義比較器類的方式實現排序。比較器程式碼如下：
// 自定義比較器：按name比較
class NameComparator implements Comparator<Person> {
@Override
public int compare(Person o1, Person o2) {
return o1.getName().compareTo(o2.getName());
}
}
// 自定義比較器：按age比較
class AgeComparator implements Comparator<Person> {
public int compare(Person object1, Person object2) {// 實現介面中的方法
return new Integer(object1.getAge()).compareTo(object2.getAge());
}
} public class T2 {
public static void main(String[] args) {
List<Person> list=new ArrayList<Person>();
Person p1=new Person("d",55);
Person p2=new Person("c",18);
Person p3=new Person("a",37);
list.add(p1);
list.add(p2);
list.add(p3);
sortPerson(list);
}
public static void sortPerson(List<Person> list){
Collections.sort(list,new NameComparator());
for (Person person : list) {
System.out.println(person);
}
}
}執行結果如下:
Person [name=a, age=37]
Person [name=c, age=18]
Person [name=d, age=55]