比较器
Arrays 类
主要功能:
- 完成所有与数组有关的操作的工具类
二分查找:
- 在一个有序的数字序列中进行二分查找
public static int binarySearch(数据类型 [] a , 数据类型 key)
案例实现
public class TestDemo {
public static void main(String [] args) throws ParseException {
int date [] = new int [] {1,4,2,5,7,4,3,8} ;
java.util.Arrays.parallelSort(date); // 排序
System.out.println(Arrays.binarySearch(date, 3)); // 二分查找
}
}
数组比较:
public static boolean equals(数据类型 [] a , 数据类型 [] b)
和Object.equals()没有任何关系,本次的arrays中的equals比较的是数组不是对象。
public class TestDemo {
public static void main(String [] args) throws ParseException {
int dateA [] = new int [] {1,4,2,5,7,4,3,8} ;
int dateB [] = new int [] {1,4,2,5,7,4,3,8} ;
System.out.println(Arrays.equals(dateA, dateB));
}
}
比较器:Comparable *
对象数组排序
public static void sort(Object [] a);
Arrays类可以直接利用 sort() 方法实现对象数组的排序
- 测试代码 *
class Book implements Comparable<Book> { //使用比较器
private String title ;
private double price ;
public Book (String title , double price) {
this.title = title ;
this.price = price ;
}
public String toString() {
return this.title + " " + this.price;
}
@Override
public int compareTo(Book o) {
// compareTo 方法由 Arrays.sort()方法自动调用
if (this.price > o.price) {
return 1 ;
} else if (this.price < o.price){
return -1 ;
} else {
return 0 ;
}
}
}
public class TestDemo {
public static void main(String [] args) throws ParseException {
Book books [] = new Book [] {
new Book("java",23),
new Book("python",20),
new Book("php",11),
new Book("C/C++",44)
} ;
Arrays.parallelSort(books);// 排序
System.out.println(Arrays.toString(books));
}
}
要对某个对象进行数组排序,对象所在的类一定要实现 Comparable 接口,覆写compareTo()方法。
二叉树结构:BinaryTree
- 数,是一种比链表更为复杂的概念,本质也属于动态对象数组,但是与链表相比,数更有利于数据进行排序。
数的操作原理
- 选择一个数据作为根节点,而后比根节点小的数据放在根节点左节点,比左节点小的放在根节点的右节点。按照 中序 进行遍历。
class Book implements Comparable<Book> { //使用比较器
private String title ;
private double price ;
public Book (String title , double price) {
this.title = title ;
this.price = price ;
}
public String toString() {
return this.title + " " + this.price;
}
@Override
public int compareTo(Book o) {
// compareTo 方法由 Arrays.sort()方法自动调用
if (this.price > o.price) {
return 1 ;
} else if (this.price < o.price){
return -1 ;
} else {
return 0 ;
}
}
}
class BinaryTree {
private class Node{
private Comparable data ;
private Node left ;
private Node right ;
public Node (Comparable data) {
this.data = data ;
}
public void addNode(Node newNode) {
if (this.data.compareTo(newNode.data) < 0 ) {
if (this.left == null) {
this.left = newNode ;
}else {
this.left.addNode(newNode);
}
}else {
if (this.right == null) {
this.right = newNode ;
} else {
this.right.addNode(newNode);
}
}
}
public void toArrayNode () {
if (this.left != null) {
this.left.toArrayNode();
}
BinaryTree.this.retData[BinaryTree.this.foot ++] = this.data;
if (this.right != null) {
this.right.toArrayNode();
}
}
}
private Node root ; // 定义根节点
private int count = 0 ;
private Object [] retData;
private int foot;
public void add(Object obj) {
Comparable com = (Comparable) obj ;// 必须转为 Comparable
Node newNode = new Node(com); //创建新的Node节点
if (this.root == null) {
this.root = newNode ;
} else {
this.root.addNode(newNode);
}
this.count ++ ;
}
public Object [] toArray(){
if (this.root ==null) {
return null;
}
this.foot = 0 ;
this.retData = new Object [this.count] ;
this.root.toArrayNode();
return this.retData;
}
}
public class TestDemo {
public static void main(String [] args) {
BinaryTree bt = new BinaryTree();
bt.add(new Book("java",23));
bt.add(new Book("python",20));
bt.add(new Book("php",11));
bt.add(new Book("C/C++",44));
Object obj [] = bt.toArray();
System.out.println(Arrays.toString(obj));
}
}
Comparator接口(下下策)
- 该接口是一个函数式接口:即只有继承方法
@FunctionalInterface
public interface Comparator<T> {
public int compare(T o1 , T o2);
public boolean equals(Object obj);
}
我们可以借助该接口,将没有实现Comparable接口的类,进行改变;
实现该接口,创建一个“工具类”,实现Book类对象的排序需求
class Book {
private String title ;
private double price ;
public Book (String title , double price) {
this.title = title ;
this.price = price ;
}
public String getTitle() {
return title;
}
public double getPrice() {
return price;
}
public void setTitle(String title) {
this.title = title;
}
public void setPrice(double price) {
this.price = price;
}
public String toString() {
return this.title + " " + this.price;
}
}
class BookComparator implements Comparator<Book>{ // 比较器工具
@Override
public int compare(Book o1, Book o2) {
if (o1.getPrice() > o2.getPrice()) {
return 1;
} else if (o1.getPrice() > o1.getPrice()){
return -1;
}else {
return 0 ;
}
}
}
public class TestDemo {
public static void main(String [] args) {
Book books [] = new Book [] {
new Book("java",23),
new Book("python",20),
new Book("php",11),
new Book("C/C++",44)
} ;
Arrays.parallelSort(books,new BookComparator());
System.out.println(Arrays.toString(books));
}
}
- 区别:
comparable是在一个类定义阶段实现的接口类,而comparator则需要专门定义一直指定的类。
总结
- 涉及到对象数组的排序,就使用Comparable接口
- 根据实际情况掌握 二叉树代码
原文地址:https://www.cnblogs.com/wangyuyang1016/p/11109725.html
时间: 2024-11-06 11:44:40