TreeSet舉例自然排序和定製排序
阿新 • • 發佈：2019-02-09
公共類:
package com.ex; import java.util.Objects; public class MyDate { private int day; private int month; private int year; public int getDay() { return day; } public void setDay(int day) { this.day = day; } public int getMonth() { return month; } public void setMonth(int month) { this.month = month; } public int getYear() { return year; } public void setYear(int year) { this.year = year; } public MyDate(int day, int month, int year) { this.day = day; this.month = month; this.year = year; } @Override public String toString() { return "MyDate{" + "day=" + day + ", month=" + month + ", year=" + year + '}'; } @Override public boolean equals(Object o) { if (this == o) return true; if (!(o instanceof MyDate)) return false; MyDate myDate = (MyDate) o; return getDay() == myDate.getDay() && getMonth() == myDate.getMonth() && getYear() == myDate.getYear(); } @Override public int hashCode() { return Objects.hash(getDay(), getMonth(), getYear()); } }
自然排序,實現comparable介面,重寫compareTo方法,按照名字排序
package com.ex; import java.util.Objects; public class Employee implements Comparable{ private String name; private int age; private MyDate birthday; 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; } public MyDate getBirthday() { return birthday; } public void setBirthday(MyDate birthday) { this.birthday = birthday; } public Employee(String name, int age, MyDate birthday) { super(); this.name = name; this.age = age; this.birthday = birthday; } @Override public String toString() { return "Employee [name=" + name + ", age=" + age + ", birthday=" + birthday + "]"; } @Override public boolean equals(Object o) { if (this == o) return true; if (!(o instanceof Employee)) return false; Employee employee = (Employee) o; return getAge() == employee.getAge() && Objects.equals(getName(), employee.getName()) && Objects.equals(getBirthday(), employee.getBirthday()); } @Override public int hashCode() { return Objects.hash(getName(), getAge(), getBirthday()); } @Override public int compareTo(Object o) { if (o instanceof Employee){ Employee e = (Employee) o; return this.name.compareTo(e.name); } return 0; } }
實現類
package com.ex; import java.util.Iterator; import java.util.TreeSet; public class TestTree { public static void main (String[] args){ //自然排序 Employee e1 = new Employee("zzz", 55, new MyDate(4, 12, 1976)); Employee e2 = new Employee("ccc", 43, new MyDate(7, 3, 1965)); Employee e3 = new Employee("ooo", 33, new MyDate(9, 12, 1954)); Employee e4 = new Employee("ppp", 54, new MyDate(12, 2, 1967)); Employee e5 = new Employee("aaa", 65, new MyDate(4, 21, 1945)); TreeSet set = new TreeSet(); set.add(e1); set.add(e2); set.add(e3); set.add(e4); set.add(e5); Iterator i = set.iterator(); while (i.hasNext()){ System.out.println(i.next()); } } }
結果
Employee [name=aaa, age=65, birthday=MyDate{day=4, month=21, year=1945}]
Employee [name=ccc, age=43, birthday=MyDate{day=7, month=3, year=1965}]
Employee [name=ooo, age=33, birthday=MyDate{day=9, month=12, year=1954}]
Employee [name=ppp, age=54, birthday=MyDate{day=12, month=2, year=1967}]
Employee [name=zzz, age=55, birthday=MyDate{day=4, month=12, year=1976}]
定製排序:java-bean沒有實現comparable介面和重寫compareTo方法
package com.ex;
import java.util.Objects;
public class Employee1 {
private String name;
private int age;
private MyDate birthday;
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;
}
public MyDate getBirthday() {
return birthday;
}
public void setBirthday(MyDate birthday) {
this.birthday = birthday;
}
public Employee1(String name, int age, MyDate birthday) {
super();
this.name = name;
this.age = age;
this.birthday = birthday;
}
@Override
public String toString() {
return "Employee [name=" + name + ", age=" + age + ", birthday="
+ birthday + "]";
}
@Override
public boolean equals(Object o) {
if (this == o) return true;
if (!(o instanceof Employee1)) return false;
Employee1 employee = (Employee1) o;
return getAge() == employee.getAge() &&
Objects.equals(getName(), employee.getName()) &&
Objects.equals(getBirthday(), employee.getBirthday());
}
@Override
public int hashCode() {
return Objects.hash(getName(), getAge(), getBirthday());
}
}
實現類
//定製排序：建立 TreeSet 時傳入 Comparator物件，按生日日期的先後排序。
package com.ex;
import java.util.Comparator;
import java.util.Iterator;
import java.util.TreeSet;
public class TestTree1 {
public static void main(String[] args) {
Comparator com = new Comparator() {
@Override
public int compare(Object o1, Object o2) {
if (o1 instanceof Employee1 && o2 instanceof Employee1) {
Employee1 e1 = (Employee1) o1;
Employee1 e2 = (Employee1) o2;
MyDate birth1 = e1.getBirthday();
MyDate birth2 = e2.getBirthday();
if (birth1.getYear() != birth2.getYear()) {
return birth1.getYear() - birth2.getYear();
} else {
if (birth1.getMonth() != birth2.getMonth()) {
return birth1.getMonth() - birth2.getMonth();
}else {
return birth1.getDay() - birth2.getDay();
}
}
}
return 0;
}
};
Employee e1 = new Employee("zzz", 55, new MyDate(4, 12, 1976));
Employee e2 = new Employee("ccc", 43, new MyDate(7, 3, 1965));
Employee e3 = new Employee("ooo", 33, new MyDate(9, 12, 1954));
Employee e4 = new Employee("ppp", 54, new MyDate(12, 2, 1967));
Employee e5 = new Employee("aaa", 65, new MyDate(4, 21, 1945));
TreeSet set = new TreeSet();
set.add(e1);
set.add(e2);
set.add(e3);
set.add(e4);
set.add(e5);
Iterator i = set.iterator();
while (i.hasNext()) {
System.out.println(i.next());
}
}
}
結果:
Employee [name=aaa, age=65, birthday=MyDate{day=4, month=21, year=1945}]
Employee [name=ccc, age=43, birthday=MyDate{day=7, month=3, year=1965}]
Employee [name=ooo, age=33, birthday=MyDate{day=9, month=12, year=1954}]
Employee [name=ppp, age=54, birthday=MyDate{day=12, month=2, year=1967}]
Employee [name=zzz, age=55, birthday=MyDate{day=4, month=12, year=1976}]