TreeMap简单simple
TreeMap能够按照主键对里面的数据进行排序，基于上篇文章：java集合类之TreeMap中有关于TreeMap内部实现的详细介绍。本文主要是写了些使用TreeMap的简单demo。
要想实现TreeMap的自动排序功能，要么主键对象实现Comparator接口，要么用Comparable来构造TreeMap。以下则分别对这两种方式创建TreeMap。
1. 继承Comparable
public class Person implements Comparable<Person>{
private String name;
private String sex;
public String getName() {
return name;
}
public void setName(String name) {
this.name = name;
}
public String getSex() {
return sex;
}
public void setSex(String sex) {
this.sex = sex;
}
@Override
public int hashCode() {
final int prime = 31;
int result = 1;
result = prime * result + ((name == null) ? 0 : name.hashCode());
result = prime * result + ((sex == null) ? 0 : sex.hashCode());
return result;
}
@Override
public boolean equals(Object obj) {
if (this == obj)
return true;
if (obj == null)
return false;
if (getClass() != obj.getClass())
return false;
Person other = (Person) obj;
if (name == null) {
if (other.name != null)
return false;
} else if (!name.equals(other.name))
return false;
if (sex == null) {
if (other.sex != null)
return false;
} else if (!sex.equals(other.sex))
return false;
return true;
}
public Person(String name, String sex) {
super();
this.name = name;
this.sex = sex;
}
@Override
public String toString() {
return "Person [name=" + name + ", sex=" + sex + "]";
}
@Override
public int compareTo(Person o) {
Person s = (Person) o;
if(this.name.compareTo(s.getName())>0){
return 1;
}else if(this.name.compareTo(s.getName())<0){
return -1;
}else {
if(this.sex.compareTo(s.getSex())>0){
return 1;
}else if(this.sex.compareTo(s.getSex()) < 0){
return -1;
}else{
return 0;
}
}
}
}
2. 实现Comparator接口
public class MyCompartor implements Comparator<Person>{
@Override
public int compare(Person o1, Person o2) {
if(null == o1){
System.out.println("o1 is null");
return 1;
}
if(null == o2){
System.out.println("o2 is null");
return -1;
}
if(o1.getName().compareTo(o2.getName())>0){
return 1;
}else if(o1.getName().compareTo(o2.getName())<0){
return -1;
}else {
if(o1.getSex().compareTo(o2.getSex())>0){
return 1;
}else if(o1.getSex().compareTo(o2.getSex()) < 0){
return -1;
}else{
return 0;
}
}
}
}
一般主键类尽量使用同一类型，如果使用不同类型则需要分别比较。
public class Student implements Comparable<Object>{
private String name;
private String sex;
public String getName() {
return name;
}
public void setName(String name) {
this.name = name;
}
public String getSex() {
return sex;
}
public void setSex(String sex) {
this.sex = sex;
}
@Override
public int hashCode() {
final int prime = 31;
int result = 1;
result = prime * result + ((name == null) ? 0 : name.hashCode());
result = prime * result + ((sex == null) ? 0 : sex.hashCode());
return result;
}
@Override
public boolean equals(Object obj) {
if (this == obj)
return true;
if (obj == null)
return false;
if (getClass() != obj.getClass())
return false;
Student other = (Student) obj;
if (name == null) {
if (other.name != null)
return false;
} else if (!name.equals(other.name))
return false;
if (sex == null) {
if (other.sex != null)
return false;
} else if (!sex.equals(other.sex))
return false;
return true;
}
public Student(String name, String sex) {
super();
this.name = name;
this.sex = sex;
}
@Override
public String toString() {
return "Student [name=" + name + ", sex=" + sex + "]";
}
@Override
public int compareTo(Object o) {
if(o instanceof Student){
Student s = (Student) o;
if(this.name.compareTo(s.getName())>0){
return 1;
}else if(this.name.compareTo(s.getName())<0){
return -1;
}else {
if(this.sex.compareTo(s.getSex())>0){
return 1;
}else if(this.sex.compareTo(s.getSex()) < 0){
return -1;
}else{
return 0;
}
}
}else if(o instanceof Person){
Person s = (Person) o;
if(this.name.compareTo(s.getName())>0){
return 1;
}else if(this.name.compareTo(s.getName())<0){
return -1;
}else {
if(this.sex.compareTo(s.getSex())>0){
return 1;
}else if(this.sex.compareTo(s.getSex()) < 0){
return -1;
}else{
return 0;
}
}
}else {
return 0;
}
}
}public class Person implements Comparable<Object>{
private String name;
private String sex;
public String getName() {
return name;
}
public void setName(String name) {
this.name = name;
}
public String getSex() {
return sex;
}
public void setSex(String sex) {
this.sex = sex;
}
@Override
public int hashCode() {
final int prime = 31;
int result = 1;
result = prime * result + ((name == null) ? 0 : name.hashCode());
result = prime * result + ((sex == null) ? 0 : sex.hashCode());
return result;
}
@Override
public boolean equals(Object obj) {
if (this == obj)
return true;
if (obj == null)
return false;
if (getClass() != obj.getClass())
return false;
Person other = (Person) obj;
if (name == null) {
if (other.name != null)
return false;
} else if (!name.equals(other.name))
return false;
if (sex == null) {
if (other.sex != null)
return false;
} else if (!sex.equals(other.sex))
return false;
return true;
}
public Person(String name, String sex) {
super();
this.name = name;
this.sex = sex;
}
@Override
public String toString() {
return "Person [name=" + name + ", sex=" + sex + "]";
}
@Override
public int compareTo(Object o) {
if(o instanceof Student){
Student s = (Student) o;
if(this.name.compareTo(s.getName())>0){
return 1;
}else if(this.name.compareTo(s.getName())<0){
return -1;
}else {
if(this.sex.compareTo(s.getSex())>0){
return 1;
}else if(this.sex.compareTo(s.getSex()) < 0){
return -1;
}else{
return 0;
}
}
}else if(o instanceof Person){
Person s = (Person) o;
if(this.name.compareTo(s.getName())>0){
return 1;
}else if(this.name.compareTo(s.getName())<0){
return -1;
}else {
if(this.sex.compareTo(s.getSex())>0){
return 1;
}else if(this.sex.compareTo(s.getSex()) < 0){
return -1;
}else{
return 0;
}
}
}else {
return 0;
}
}
}测试：
public class TreeMapExample {
@Test
public void test1(){
TreeMap<Object, Object> treeMap = new TreeMap<Object, Object>();//主键不同类型
Student s1 = new Student("a", "m");
Student s2 = new Student("a", "c");
Person p1 = new Person("d", "w");
Person p2 = new Person("b", "m");
treeMap.put(s1, s1);
treeMap.put(s2, s2);
treeMap.put(p1, p1);
treeMap.put(p2, p2);
for(Map.Entry<Object, Object> entry : treeMap.entrySet()){
System.out.println(entry.getKey().toString());
}
}
@Test
public void test2(){
MyCompartor compartor = new MyCompartor();
TreeMap<Person, Person> treeMap = new TreeMap<Person, Person>(compartor);//主键中放入null
Person s1 = new Person("a", "m");
Person s2 = new Person("a", "c");
Person p1 = new Person("d", "w");
Person p2 = new Person("b", "m");
Person p3 = new Person("b", "c");
treeMap.put(s1, s1);
treeMap.put(s2, s2);
treeMap.put(p1, p1);
treeMap.put(p2, p2);
treeMap.put(null, p3);
System.out.println(treeMap.size());
for(Map.Entry<Person, Person> entry : treeMap.entrySet()){
System.out.println(entry.getKey()+":"+entry.getValue());
}
}
}
