java - object==object，不比较引用

Question

我已经覆盖了哈希码和 equals 以找到具有相同 startDate 和 closingDate 的值。而且我得到了重复对象的类似哈希码。当等同于这些对象时，我得到 boolean 值“false”。在我的理解中，object==object 比较对象的引用，即使引用相同；代码返回 false。你能帮我理解问题是什么吗？我在下面发布了我的代码:

Hashcode & equals 方法

public int hashCode() {
    final int prime = 31; 
    int result = 1;
    result = prime * result + ((this.startDate == null) ? 0 : this.startDate.getDate());
    result = prime * result + ((this.closingDate == null) ? 0 : this.closingDate.getDate());
    return result;
}

public boolean equals(Object customer) {
    if(customer == null || customer.getClass()!= this.getClass())
        return false;

    return this==customer;
}

主.java

public class HashQuestion {
    public static void main(String[]args) {
        Map<Integer, Customer> custMap = new HashMap<Integer, Customer>();
        custMap.put(1, createCustomer(1, new Date()));
        custMap.put(2, createCustomer(2, new Date()));
        custMap.put(3, createCustomer(3, new Date()));
        Customer checkCustomer = createCustomer(1, new Date());
        for (Customer cust : custMap.values()) {

            if (cust.equals(checkCustomer)) {
                System.out.println("Duplicate No: "+cust.getCustId()+ ", Start date: " + 
                        cust.getStartDate().toString() + " End date: " +cust.getClosingDate().toString());
            }
            else
                System.out.println("No: "+cust.getCustId()+ ", Start date: " + 
                    cust.getStartDate().toString() + " End date: " +cust.getClosingDate().toString());
        } 
    }

    @SuppressWarnings("deprecation")
    static Customer createCustomer(int number, Date date) {
        Date closeDate = new Date(); 
        Date startDate = new Date(); 
        closeDate.setDate(date.getDate() + number);
        startDate.setDate(date.getDate() - number);
        return new Customer(number, number+1, startDate, closeDate);
    }
}

输出:

No: 1, Start date: Wed Jun 20 19:42:46 IST 2018 End date: Fri Jun 22 19:42:46 IST 2018
No: 2, Start date: Tue Jun 19 19:42:46 IST 2018 End date: Sat Jun 23 19:42:46 IST 2018
No: 3, Start date: Mon Jun 18 19:42:46 IST 2018 End date: Sun Jun 24 19:42:46 IST 2018

检查客户对象引用:Customer@643

对象引用(在 map 中):[Customer@643, Customer@625, Customer@607]

此处 object1 与 checkCustomer obj 具有相同的引用。但是 obj==checkCustomer，返回 false。

Answer 1

由此改变:

Map<Integer, Customer> custMap = new HashMap<Integer, Customer>();
custMap.put(1, createCustomer(1, new Date()));
custMap.put(2, createCustomer(2, new Date()));
custMap.put(3, createCustomer(3, new Date()));
Customer checkCustomer = createCustomer(1, new Date()); //This is a different reference

对此:

Map<Integer, Customer> custMap = new HashMap<Integer, Customer>();
Customer checkCustomer = createCustomer(1, new Date());
custMap.put(1, checkCustomer); //Now this is the same reference
custMap.put(2, createCustomer(2, new Date()));
custMap.put(3, createCustomer(3, new Date()));

您正在创建 4 个不同的客户，这将创建三个。