TreeSet实现自动排序的原理

今天随手了一段代码关于通过treeSet实现自动排序的功能，自己折腾了好久。

始终是存在这一些疑惑，后来和同学的交流和调试可以解释自动排序的基本原理：

通过可以通过两种方式实现自动排序：

一种：

package xyxysjxy.io;

import java.io.BufferedReader;
import java.io.BufferedWriter;
import java.io.FileWriter;
import java.io.IOException;
import java.io.InputStreamReader;
import java.util.Comparator;
import java.util.Iterator;
import java.util.Set;
import java.util.TreeSet;

public class StudentInfoImport {

	public static void main(String[] args) throws IOException {
		BufferedWriter bw = new BufferedWriter(
				new FileWriter("f:\\student.txt"));
		Set<Student> ss = StudentTools.getStudent();
		Iterator<Student> is = ss.iterator();
		while (is.hasNext()) {
			Student student = (Student) is.next();
			bw.write(student.toString());
			bw.newLine();
			bw.flush();
		}
		bw.close();
	}

}

class Student{
	private String name;
	private int cn;
	private int math;
	private int en;
	private int sum;

	public String getName() {
		return name;
	}

	public void setName(String name) {
		this.name = name;
	}

	public int getCn() {
		return cn;
	}

	public void setCn(int cn) {
		this.cn = cn;
	}

	public int getMath() {
		return math;
	}

	public void setMath(int math) {
		this.math = math;
	}

	public int getEn() {
		return en;
	}

	public void setEn(int en) {
		this.en = en;
	}

	public int getSum() {
		return sum;
	}

	public void setSum(int sum) {
		this.sum = sum;
	}

	public Student(String name, int... is) {
		this.name = name;
		this.cn = is[0];
		this.math = is[1];
		this.en = is[2];
		this.sum = cn + math + en;
	}

	@Override
	public String toString() {
		return "【name=" + name + "\tcn=" + cn + "\tmath=" + math + "\ten=" + en
				+ "\tsum=" + sum + "】";
	}

	@Override
	public boolean equals(Object obj) {
		if (!(obj instanceof Student))
			throw new ClassCastException("不能强制的转换");
		Student s = (Student) obj;
		return s.name.equals(this.name) && s.sum == s.sum;
	}

	@Override
	public int hashCode() {
		return sum * 78 + name.hashCode();
	}

}

class StudentTools {
	static Comparator<Student> com = new Comparator<Student>() {

		@Override
		public int compare(Student o1, Student o2) {
			int sum = new Integer(o1.getSum()).compareTo(new Integer(o2.getSum()));
			if (sum == 0)
				return o1.getName().compareTo(o2.getName());
			return sum;
		}

	};

	public static Set<Student> getStudent() throws IOException {
		return getStudent(com);
	}

	public static Set<Student> getStudent(Comparator<Student> com)
			throws IOException {
		Set<Student> studentSet = null;
		if (com == null)
			studentSet = new TreeSet<Student>();
		else
			studentSet = new TreeSet<Student>(com);

		BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
		String len = "";
		while ((len = br.readLine()) != null) {
			if (len.equals("over"))
				break;
			String[] studentInfo = len.split(",");

			Student s = new Student(studentInfo[0], new int[] {
					Integer.parseInt(studentInfo[1]),
					Integer.parseInt(studentInfo[2]),
					Integer.parseInt(studentInfo[3]) });
			// 当往HashSet中添加数据时，他会去找被添加对象的中实现了Comparable接口，
			studentSet.add(s);
		}
		return studentSet;

	}
}

二种：

package xyxysjxy.io;

import java.io.BufferedReader;
import java.io.BufferedWriter;
import java.io.FileWriter;
import java.io.IOException;
import java.io.InputStreamReader;
import java.util.Comparator;
import java.util.Iterator;
import java.util.Set;
import java.util.TreeSet;

public class StudentInfoImport {

	public static void main(String[] args) throws IOException {
		BufferedWriter bw = new BufferedWriter(
				new FileWriter("f:\\student.txt"));
		Set<Student> ss = StudentTools.getStudent();
		Iterator<Student> is = ss.iterator();
		while (is.hasNext()) {
			Student student = (Student) is.next();
			bw.write(student.toString());
			bw.newLine();
			bw.flush();
		}
		bw.close();
	}

}

class Student implements Comparable<Student> {
	private String name;
	private int cn;
	private int math;
	private int en;
	private int sum;

	public Student(String name, int... is) {
		this.name = name;
		this.cn = is[0];
		this.math = is[1];
		this.en = is[2];
		this.sum = cn + math + en;
	}

	@Override
	public String toString() {
		return "【name=" + name + "\tcn=" + cn + "\tmath=" + math + "\ten=" + en
				+ "\tsum=" + sum + "】";
	}

	@Override
	public boolean equals(Object obj) {
		if (!(obj instanceof Student))
			throw new ClassCastException("不能强制的转换");
		Student s = (Student) obj;
		return s.name.equals(this.name) && s.sum == s.sum;
	}

	public int compareTo(Student o) {
		int sum = new Integer(this.sum).compareTo(new Integer(o.sum));
		if (sum == 0)
			return this.name.compareTo(o.name);
		return sum;
	}

	@Override
	public int hashCode() {
		return sum * 78 + name.hashCode();
	}

}

class StudentTools {
	public static Set<Student> getStudent() throws IOException {
		return getStudent(null);
	}

	public static Set<Student> getStudent(Comparator<Student> com)
			throws IOException {
		Set<Student> studentSet = null;
		if (com == null)
			studentSet = new TreeSet<Student>();
		else
			studentSet = new TreeSet<Student>(com);

		BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
		String len = "";
		while ((len = br.readLine()) != null) {
			if (len.equals("over"))
				break;
			String[] studentInfo = len.split(",");

			Student s = new Student(studentInfo[0], new int[] {
					Integer.parseInt(studentInfo[1]),
					Integer.parseInt(studentInfo[2]),
					Integer.parseInt(studentInfo[3]) });		<pre name="code" class="java">// 当往HashSet中添加数据时，他会去找被添加对象的中实现了Comparable接口，
			studentSet.add(s);
		}
		return studentSet;

	}
}

通过上面的两段代码把这个执行的流程给大家讲解一下：

第一步：从控制台接收数值后封装到了一个student对象当中去。

              其实在treeSet内部其实封装了一个TreeMap对象

当你调用了ADD方法时其实是调用了put方法。

<pre name="code" class="java">while ((len = br.readLine()) != null) {
			if (len.equals("over"))
				break;
			String[] studentInfo = len.split(",");

			Student s = new Student(studentInfo[0], new int[] {
					Integer.parseInt(studentInfo[1]),
					Integer.parseInt(studentInfo[2]),
					Integer.parseInt(studentInfo[3]) });			<pre name="code" class="java">              // 当往HashSet中添加数据时，他会去找被添加对象的中实现了Comparable接口，
			studentSet.add(s);
		}
		return studentSet;

public TreeSet(Comparator<? super E> comparator) { this(new TreeMap<>(comparator)); }

第二步：首先他要进行检查。

               这个三目运算符是这个意思：

              首先他是判断你在new treeset时候是否向其中传递了一个 comparator

               对象，假如传递了那么直接调用你传进来的那个对象

              但是你没有传递进来那么他就要做类型检查了，

             检查的目的在与看你是否实现了Comparable假如实现了那么就调用你自身的实现接口的方法

<strong></strong><pre name="code" class="java">public V put(K key, V value) {
        Entry<K,V> t = root;
        if (t == null) {
            compare(key, key); // type (and possibly null) check(L类型检查)

            root = new Entry<>(key, value, null);
            size = 1;
            modCount++;
            return null;
        }

//其实在第一次存储对象时，所进行的比较是和自身比较 compare(key, key)
final int compare(Object k1, Object k2) {
     return comparator==null ? ((Comparable<? super K>)k1).compareTo((K)k2) : comparator.compare((K)k1, (K)k2); } 

第三步: 当检查到你是实现了compare接口或是传递了一个compator对象时，

             他会调用你自身的实现方法进行比较。

             通过返回值：-1，0，1来判断你正要假如的值和treeset中的大小进行自动的排序的效果。

TreeSet实现自动排序的原理