@overriding equals() 和 hashCode() 在 Java class

Question

我有一个示例 Java class 银行账户：

public class Account {
    private Integer accountNumber;
    private Integer authPin;
    private Integer transactionPin;

    public Account(Integer accountNumber, Integer authPin, Integer transactionPin) {
        this.accountNumber = accountNumber;
        this.authPin = authPin;
        this.transactionPin = transactionPin;
    }

    public Integer getAccountNumber() {
        return accountNumber;
    }

    public void setAccountNumber(Integer accountNumber) {
        this.accountNumber = accountNumber;
    }

    public Integer getAuthPin() {
        return authPin;
    }

    public void setAuthPin(Integer authPin) {
        this.authPin = authPin;
    }

    public Integer getTransactionPin() {
        return transactionPin;
    }

    public void setTransactionPin(Integer transactionPin) {
        this.transactionPin = transactionPin;
    }

    @Override
    public String toString() {
        return accountNumber + "," + authPin + "," + transactionPin;
    }

    @Override
    public boolean equals(Object obj) {
        Account account = (Account) obj;
        return (this.accountNumber == account.getAccountNumber() && this.authPin == account.getAuthPin()
                && this.transactionPin == account.getTransactionPin());
    }

    @Override
    public int hashCode() {
        // TODO Auto-generated method stub
        return Objects.hashCode(this.getAccountNumber());
    }
}

从代码片段可以看出，我重写了equals() 和hashCode() 方法。但是当我尝试使用 jUnit 进行简单的断言检查时，它失败了：

public class TestFileIO {
    Account account;

    @Before
    public void setUp() throws Exception {
        account = new Account(7, 2708, 2708);
    }

    @Test
    public void testReadTransactionFile() {
        assertEquals(account, new Account(7, 2708, 2708));
    }

我是不是漏掉了什么重要的东西？

Answer 1

而不是比较 Integer 对象引用：

return (this.accountNumber == account.getAccountNumber() && this.authPin == account.getAuthPin()
        && this.transactionPin == account.getTransactionPin());

因为，Integer 对象引用 不等于 ，例如这个断言失败：

// different identities -> this assertion fails
assert new Integer(7) == new Integer(7);

使用.equals:

return (Objects.equals(this.accountNumber, account.getAccountNumber())
        && Objects.equals(this.authPin, account.getAuthPin())
        && Objects.equals(this.transactionPin, account.getTransactionPin()));

如果字段保证永远不会是 null，则将它们的类型更改为 int:

private int accountNumber;
private int authPin;
private int transactionPin;

那么您就不需要更改 equals 实现，因为它已经很好了。

@overriding equals() 和 hashCode() 在 Java class

@overriding equals() and hashCode() in Java class

java

equals

hashcode

junit4