Override equals Code

来源：互联网发布：cn 域名编辑：程序博客网时间：2024/05/14 06:01

我想告诉自己的是：对于所有对象都通用的方法 equals，需要重构。

根据每一个对象特殊的业务判断，我们需要重构这些通用的方法。

因为底层的equals实际上并不满足我们，有的时候，调用后，并不知道里面的真实结果。

Democreen cis = new Democreen("Polish");        String s = "polish";        System.out.println(cis.equals(s) + "  " + s.equals(cis));

console控制台：

DemocreenConnected to the target VM, address: '127.0.0.1:58575', transport: 'socket'Disconnected from the target VM, address: '127.0.0.1:58575', transport: 'socket'true  falseProcess finished with exit code 0

Democreen.java中

@Override public boolean equals(Object o) {        if (o instanceof Democreen)            return s.equalsIgnoreCase(                    ((Democreen) o).s);        if (o instanceof String)  // One-way interoperability!            return s.equalsIgnoreCase((String) o);        return false;    }

String.java源码：

/**     * Compares this string to the specified object.  The result is {@code     * true} if and only if the argument is not {@code null} and is a {@code     * String} object that represents the same sequence of characters as this     * object.     *     * @param  anObject     *         The object to compare this {@code String} against     *     * @return  {@code true} if the given object represents a {@code String}     *          equivalent to this string, {@code false} otherwise     *     * @see  #compareTo(String)     * @see  #equalsIgnoreCase(String)     */    public boolean equals(Object anObject) {if (this == anObject) {    return true;}if (anObject instanceof String) {    String anotherString = (String)anObject;    int n = count;    if (n == anotherString.count) {char v1[] = value;char v2[] = anotherString.value;int i = offset;int j = anotherString.offset;while (n-- != 0) {    if (v1[i++] != v2[j++])return false;}return true;    }}return false;    }

事实上，我们队实例去比较的时候，可以通过重构equals来提高代码性能跟质量：

public boolean equals(Object obj) {        if (this == obj) {            return true;        }        if (obj != null && obj instanceof Entity) {            Entity tempObj = (Entity) obj;            return new EqualsBuilder()                    .append(getId(), tempObj.getId())                    .isEquals();        } else {            return false;        }    }

是否对称的，传递的，一致的，自反性的，非空性的，如果不具备，重新完善，需要自己不断测试优化。

覆盖equals时，总要覆盖 hasCode

见另一篇：覆盖equals时总要覆盖hasCode

0 0