TreeSet、Comparable、Comparator、內部類、匿名類
阿新 • • 發佈：2018-12-26
1 package com.tn.treeSet; 2 3 public class Student { 4 private String name; 5 private int age; 6 public Student(){} 7 public Student(String name, int age) { 8 super(); 9 this.name = name; 10 this.age = age; 11 } 12 public String getName() {13 return name; 14 } 15 public void setName(String name) { 16 this.name = name; 17 } 18 public int getAge() { 19 return age; 20 } 21 public void setAge(int age) { 22 this.age = age; 23 } 24 @Override 25 public String toString() { 26 return"Student [name=" + name + "]"; 27 } 28 }
1 package com.tn.treeSet; 2 3 import java.util.TreeSet; 4 5 public class TreeSetDemo { 6 public static void main(String[] args){ 7 TreeSet<Student> students=new TreeSet<>();//後一個尖括號內可以省略型別 8 Student student1=newStudent("武松",30); 9 Student student2=new Student("林沖",31); 10 Student student3=new Student("魯智深",29); 11 students.add(student1); 12 students.add(student2); 13 students.add(student3); 14 System.out.println(students); 15 } 16 }
執行結果：
原因:TreeSet中加入的物件需要能進行比較，即實現Comparable介面
改造一：在Student類中實現Comparable介面
1 package com.tn.treeSet; 2 3 public class Student implements Comparable<Student> { 4 private String name; 5 private int age; 6 public Student(){} 7 public Student(String name, int age) { 8 super(); 9 this.name = name; 10 this.age = age; 11 } 12 public String getName() { 13 return name; 14 } 15 public void setName(String name) { 16 this.name = name; 17 } 18 public int getAge() { 19 return age; 20 } 21 public void setAge(int age) { 22 this.age = age; 23 } 24 @Override 25 public String toString() { 26 return "Student [name=" + name + "]"; 27 } 28 @Override 29 public int compareTo(Student o) { 30 if(!this.equals(o)){ 31 // return this.name.compareTo(o.name); 32 return o.name.compareTo(this.name);//和上面語句列印順序顛倒。 33 } 34 return 0; 35 } 36 }
1 package com.tn.treeSet; 2 3 import java.util.TreeSet; 4 5 public class TreeSetDemo { 6 public static void main(String[] args){ 7 TreeSet<Student> students=new TreeSet<>();//後一個尖括號內可以省略型別 8 Student student1=new Student("武松",30); 9 Student student2=new Student("林沖",31); 10 Student student3=new Student("魯智深",29); 11 students.add(student1); 12 students.add(student2); 13 students.add(student3); 14 System.out.println(students); 15 };//方法體結結尾大括號後有;不會報錯 16 };//類體最後一個大括號後有;不會報錯
改造二：用內部類實現Comparator介面
1 package com.tn.treeSet; 2 3 public class Student{ 4 private String name; 5 private int age; 6 public Student(){} 7 public Student(String name, int age) { 8 super(); 9 this.name = name; 10 this.age = age; 11 } 12 public String getName() { 13 return name; 14 } 15 public void setName(String name) { 16 this.name = name; 17 } 18 public int getAge() { 19 return age; 20 } 21 public void setAge(int age) { 22 this.age = age; 23 } 24 @Override 25 public String toString() { 26 return "Student [name=" + name + "]"; 27 } 28 }
1 package com.tn.treeSet; 2 3 import java.util.Comparator; 4 import java.util.TreeSet; 5 6 public class TreeSetDemo { 7 public static void main(String[] args){ 8 Student student1=new Student("武松",30); 9 Student student2=new Student("林沖",31); 10 Student student3=new Student("魯智深",29); 11 //TreeSet構造時用Comparator作為建構函式引數 12 TreeSet<Student> students=new TreeSet<Student>(new ComparatorDemo()); 13 students.add(student1); 14 students.add(student2); 15 students.add(student3); 16 System.out.println(students); 17 } 18 static class ComparatorDemo implements Comparator<Student>{ 19 // 內部類要寫在類體裡，但不能寫進類中方法體內。 20 @Override 21 public int compare(Student o1, Student o2) { 22 return o1.getName().compareTo(o2.getName()); 23 } 24 } 25 }
改造三：用匿名類實現Comparator介面
1 package com.tn.treeSet; 2 3 public class Student{ 4 private String name; 5 private int age; 6 public Student(){} 7 public Student(String name, int age) { 8 super(); 9 this.name = name; 10 this.age = age; 11 } 12 public String getName() { 13 return name; 14 } 15 public void setName(String name) { 16 this.name = name; 17 } 18 public int getAge() { 19 return age; 20 } 21 public void setAge(int age) { 22 this.age = age; 23 } 24 @Override 25 public String toString() { 26 return "Student [name=" + name + "]"; 27 } 28 }
1 package com.tn.treeSet; 2 3 import java.util.Comparator; 4 import java.util.TreeSet; 5 6 public class TreeSetDemo { 7 public static void main(String[] args) { 8 Student student1 = new Student("武松", 30); 9 Student student2 = new Student("林沖", 31); 10 Student student3 = new Student("魯智深", 29); 11 12 TreeSet<Student> students = new TreeSet<Student>( 13 new Comparator<Student>() { 14 @Override 15 public int compare(Student o1, Student o2) { 16 return o1.getName().compareTo(o2.getName()); 17 } 18 }); 19 students.add(student1); 20 students.add(student2); 21 students.add(student3); 22 System.out.println(students); 23 } 24 }
總結：
TreeSet容器中的物件要能排序，兩種實現排序方法：
1.TreeSet使用無參建構函式，容器中的物件實現Comparable介面，見改造一；
2.TreeSet構造時使用Comparator作為建構函式引數；
比較方法如果返回0，則物件不能重複加入。
TreeSet底層是TreeMap