java学习日记 比较器

一、回顾Arrays类（了解）

import java.util.Arrays;

public class ArraysDemo1 {
    public static void main(String[] args) {
        int [] arr = new int[]{5,3,2,4,3,6};
        Arrays.sort(arr);
        System.out.println(Arrays.binarySearch(arr,3));
        int [] arr2 = new int[]{3,2,4,3,6,5};
        int [] arr3 = new int[]{2,3,3,4,5,6};  
        System.out.println(Arrays.equals(arr,arr2));
        System.out.println(Arrays.equals(arr,arr3));
    }
}

运行结果：

2
false
true

2、Comparable接口

import java.util.Arrays;

class ArrayCom implements Comparable<ArrayCom>{
    private String title;
    private double price;
    public ArrayCom(String title,double price){
        this.title = title;
        this.price = price;
    }

    @Override
    public String toString() {
        return "title="+this.title+",price="+this.price+"\n";
    }

    @Override
    public int compareTo(ArrayCom o) {  //Arrays.sort会自动调用
        if (this.price>o.price){
            return 1;
        }else if (this.price<o.price){
            return -1;
        }else {
            return 0;
        }
    }
}
public class ComparableDemo1 {
    public static void main(String[] args) {
        ArrayCom arr1 = new ArrayCom("java",78.3);
        ArrayCom arr2 = new ArrayCom("oracle",52.2);
        ArrayCom arr3 = new ArrayCom("c",99.99);
        ArrayCom [] arr =new ArrayCom[]{arr1,arr2,arr3};
        Arrays.sort(arr);
        System.out.println(Arrays.toString(arr));
    }
}

运行结果：

[title=oracle,price=52.2
, title=java,price=78.3
, title=c,price=99.99
]

3、数据结构——二叉树（BinaryTree）

class BinaryTree{
    class Node{
        private Node left;
        private Node right;
        private Comparable data;
        public void addNode(Node node){
            //确定是放左子树还是右子树
            if (node.data.compareTo(this.data)<0){
                if (this.left == null){
                    this.left = node;
                }else {
                    this.left.addNode(node);
                }
            }
            if (node.data.compareTo(this.data)>=0){
                if (this.right == null){
                    this.right = node;
                }else {
                    this.right.addNode(node);
                }
            }
            if (node == null){
                return;
            }
        }
        public void printNode(){
            if (this.left!=null){
                this.left.printNode();
            }
            System.out.println(this.data+"\t");
            if (this.right!=null){
                this.right.printNode();
            }
        }
    }
    private Node root;
    public void add(Comparable data){
        Node newNode = new Node();
        newNode.data = data;
        if (root == null){
            root = newNode;
        }else {
            root.addNode(newNode);
        }
    }
    public void print(){
        this.root.printNode();
    }
}
class ArrayCom implements Comparable<ArrayCom>{
    private String title;
    private double price;
    public ArrayCom(String title,double price){
        this.title = title;
        this.price = price;
    }

    @Override
    public String toString() {
        return "title="+this.title+",price="+this.price+"\n";
    }

    @Override
    public int compareTo(ArrayCom o) {  //Arrays.sort会自动调用
        if (this.price>o.price){
            return 1;
        }else if (this.price<o.price){
            return -1;
        }else {
            return 0;
        }
    }
}
public class ComparableDemo1 {
    public static void main(String[] args) {
        ArrayCom arr1 = new ArrayCom("java",78.3);
        ArrayCom arr2 = new ArrayCom("oracle",52.2);
        ArrayCom arr3 = new ArrayCom("c",99.99);
        ArrayCom arr4 = new ArrayCom("jsp",66.6);
        BinaryTree binaryTree = new BinaryTree();
        binaryTree.add(arr1);
        binaryTree.add(arr2);
        binaryTree.add(arr3);
        binaryTree.add(arr4);
        binaryTree.print();
    }
}

运行结果：

title=oracle,price=52.2
    
title=jsp,price=66.6
    
title=java,price=78.3
    
title=c,price=99.99

4、挽救的比较器Comparator

class ArrayCom {
    private String title;
    private double price;

    public String getTitle() {
        return title;
    }

    public void setTitle(String title) {
        this.title = title;
    }

    public double getPrice() {
        return price;
    }

    public void setPrice(double price) {
        this.price = price;
    }

    public ArrayCom(String title, double price){
        this.title = title;
        this.price = price;
    }

    @Override
    public String toString() {
        return "title="+this.title+",price="+this.price+"\n";
    }
}
class ArrayComparator implements Comparator<ArrayCom>{

    @Override
    public int compare(ArrayCom o1, ArrayCom o2) {
        if (o1.getPrice()>o2.getPrice()){
            return 1;
        }else if (o1.getPrice()<o2.getPrice()){
            return -1;
        }else {
            return 0;
        }
    }
}
public class ComparableDemo1 {
    public static void main(String[] args) {
        ArrayCom arr1 = new ArrayCom("java",78.3);
        ArrayCom arr2 = new ArrayCom("oracle",52.2);
        ArrayCom arr3 = new ArrayCom("c",99.99);
        ArrayCom arr4 = new ArrayCom("jsp",66.6);

        ArrayCom [] arr = new ArrayCom[]{arr1,arr2,arr3,arr4};
        Arrays.sort(arr,new ArrayComparator());
        System.out.println(Arrays.toString(arr));

    }
}

Comparable和Comparator的区别？

Comparable是一个类定义的时候实现好的接口，实现了Comparable接口的类有一个特点，就是这些类是可以和自己比较的，依赖compareTo方法的实现。

Comparator是专门定义一个指定类的比较规则，有两个方法一个是compare()，一个是equals()。