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정렬을 위해 Comparable, Comparator 인터페이스 구현
TreeSet 클래스 활용
- 객체의 정렬에 사용하는 클래스
- Set 인터페이스를 구현하여 중복을 허용하지 않고, 오름차순이나 내림차순으로 객체를 정렬할 수 있음
- 내부적으로 이진검색트리(binary search tree)로 구현됨
- 이진검색트리에 저장하기 위해 각 객체를 비교해야 함
- 비교 대상이 되는 객체에 Comparable이나 Comparator 인터페이스를 구현 해야 TreeSet에 추가 될 수 있음
- String, Integer등 JDK의 많은 클래스들이 이미 Comparable을 구현했다
Comparable 이용
package ch49;
public class Member implements Comparable<Member> {
private int memberId; // 회원 아이디
private String memberName; // 회원 이름
public Member(int memberId, String memberName) { // 생성자
this.memberId = memberId;
this.memberName = memberName;
}
public int getMemberId() { //
return memberId;
}
public void setMemberId(int memberId) {
this.memberId = memberId;
}
public String getMemberName() {
return memberName;
}
public void setMemberName(String memberName) {
this.memberName = memberName;
}
@Override
public int hashCode() {
return memberId;
}
@Override
public boolean equals(Object obj) {
if (obj instanceof Member) { // Member 클래스 인지 확인
Member member = (Member) obj; // Member 클래스로 다운 캐스팅
if (this.memberId == member.memberId) { // 기존 memberId 와 같은 값이 있는지 확인
return true;
} else {
return false;
}
}
return false;
}
@Override
public String toString() { // toString 메소드 오버로딩
return memberName + " 회원님의 아이디는 " + memberId + "입니다";
}
@Override
public int compareTo(Member member) {
// if (this.memberId > member.memberId) {
// return 1;
// } else if (this.memberId < member.memberId) {
// return -1;
// } else {
// return 0;
// }
return (this.memberId - member.memberId);
}
}
package ch49;
import java.util.HashSet;
import java.util.Iterator;
import java.util.TreeSet;
public class MemberTreeSet {
private TreeSet<Member> treeSet;
public MemberTreeSet() {
treeSet = new TreeSet<>();
}
public void addMember(Member member) {
treeSet.add(member);
}
public boolean removeMember(int memberId) {
Iterator<Member> ir = treeSet.iterator();
while(ir.hasNext()) {
Member member = ir.next();
if (member.getMemberId() == memberId) {
treeSet.remove(member);
return true;
}
}
System.out.println(memberId + "가 존재하지 않습니다");
return false;
}
public void showAllMember() {
for (Member member : treeSet) {
System.out.println(member);
}
System.out.println();
}
}
package ch49;
import java.util.TreeSet;
public class MemberTreeSetTest {
public static void main(String[] args) {
TreeSet<String> set = new TreeSet<>();
set.add("홍길동");
set.add("강감찬");
set.add("이순신");
System.out.println(set); // 정렬되어 나옴
MemberTreeSet memberTreeSet = new MemberTreeSet();
Member memberHong = new Member(1004, "홍길동");
Member memberLee = new Member(1001, "이순신");
Member memberKim = new Member(1002, "김유신");
Member memberKang = new Member(1003, "강감찬");
memberTreeSet.addMember(memberHong);
memberTreeSet.addMember(memberLee);
memberTreeSet.addMember(memberKim);
memberTreeSet.addMember(memberKang);
memberTreeSet.showAllMember();
memberTreeSet.removeMember(memberKang.getMemberId());
memberTreeSet.showAllMember();
//
}
}
Comparator의 활용: 이미 Comparable이 구현된 경우 Comparator로 비교하는 방식을 다시 구현할 수 있음
package ch49;
import java.util.Comparator;
import java.util.TreeSet;
public class Member implements Comparator<Member> {
private int memberId; // 회원 아이디
private String memberName; // 회원 이름
public Member(int memberId, String memberName) { // 생성자
this.memberId = memberId;
this.memberName = memberName;
}
public Member() {
}
public int getMemberId() { //
return memberId;
}
public void setMemberId(int memberId) {
this.memberId = memberId;
}
public String getMemberName() {
return memberName;
}
public void setMemberName(String memberName) {
this.memberName = memberName;
}
@Override
public int hashCode() {
return memberId;
}
@Override
public boolean equals(Object obj) {
if (obj instanceof Member) { // Member 클래스 인지 확인
Member member = (Member) obj; // Member 클래스로 다운 캐스팅
if (this.memberId == member.memberId) { // 기존 memberId 와 같은 값이 있는지 확인
return true;
} else {
return false;
}
}
return false;
}
@Override
public String toString() { // toString 메소드 오버로딩
return memberName + " 회원님의 아이디는 " + memberId + "입니다";
}
// 비교 후 오름차순 정렬
// @Override
// public int compareTo(Member member) {
//
//// if (this.memberId > member.memberId) {
//// return 1;
//// } else if (this.memberId < member.memberId) {
//// return -1;
//// } else {
//// return 0;
//// }
//
// return (this.memberId - member.memberId);
// }
@Override
public int compare(Member member1, Member member2) {
// TODO Auto-generated method stub
return (member1.memberId - member2.memberId);
}
}
package ch49;
import java.util.HashSet;
import java.util.Iterator;
import java.util.TreeSet;
public class MemberTreeSet {
private TreeSet<Member> treeSet;
public MemberTreeSet() {
treeSet = new TreeSet<Member>(new Member());
}
public void addMember(Member member) {
treeSet.add(member);
}
public boolean removeMember(int memberId) {
Iterator<Member> ir = treeSet.iterator();
while(ir.hasNext()) {
Member member = ir.next();
if (member.getMemberId() == memberId) {
treeSet.remove(member);
return true;
}
}
System.out.println(memberId + "가 존재하지 않습니다");
return false;
}
public void showAllMember() {
for (Member member : treeSet) {
System.out.println(member);
}
System.out.println();
}
}
package ch49;
import java.util.Comparator;
import java.util.TreeSet;
class MyCompare implements Comparator<String> {
@Override
public int compare(String s1, String s2) {
return s1.compareTo(s2) * -1;
}
}
public class MemberTreeSetTest {
public static void main(String[] args) {
/*
TreeSet<String> set = new TreeSet<>();
set.add("홍길동");
set.add("강감찬");
set.add("이순신");
System.out.println(set); // 정렬되어 나옴
MemberTreeSet memberTreeSet = new MemberTreeSet();
Member memberHong = new Member(1004, "홍길동");
Member memberLee = new Member(1001, "이순신");
Member memberKim = new Member(1002, "김유신");
Member memberKang = new Member(1003, "강감찬");
memberTreeSet.addMember(memberHong);
memberTreeSet.addMember(memberLee);
memberTreeSet.addMember(memberKim);
memberTreeSet.addMember(memberKang);
memberTreeSet.showAllMember();
memberTreeSet.removeMember(memberKang.getMemberId());
memberTreeSet.showAllMember();
*/
TreeSet<String> set = new TreeSet<>(new MyCompare());
set.add("Park");
set.add("Kim");
set.add("Lee");
System.out.println(set);
}
}
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