光子CI之旅

既然Effective Java和Guava都诞生于Google，那么当他们相遇会什么样呢，为此我决定重温Effective Java这部著作，并针对每一条规则寻找Guava给出的解决方案，希望能更深入的掌握Java。

Effective Java第10条规则： 始终要覆盖toString方法

Effective Java里指出，"建议所有的子类都覆盖这个toString方法"，这样可以使类用起来更加舒适。最重要的是这样的做法对调试非常有帮助，Guava通过 Objects.toStringHelper为我们提供了方便创建toString的方法。看下面的样例：

// Returns "ClassName{x=1}"
   Objects.toStringHelper(this)
       .add("x", 1)
       .toString();

   // Returns "MyObject{x=1}"
   Objects.toStringHelper("MyObject")
       .add("x", 1)
       .toString();

Guava关于toString的文档连接： https://code.google.com/p/guava-libraries/wiki/CommonObjectUtilitiesExplained

下面我把Effective Java的样例代码列出，并用Guava重新了toString方法

// 重写PhoneNumber的toString方法 - Effective Java中文第二版第44页
package org.effectivejava.examples.chapter03.item10;

import java.util.HashMap;
import java.util.Map;

import com.google.common.base.Objects;

public final class PhoneNumber {
        private final short areaCode;
        private final short prefix;
        private final short lineNumber;

        public PhoneNumber(int areaCode, int prefix, int lineNumber) {
                rangeCheck(areaCode, 999, "area code");
                rangeCheck(prefix, 999, "prefix");
                rangeCheck(lineNumber, 9999, "line number");
                this.areaCode = (short) areaCode;
                this.prefix = (short) prefix;
                this.lineNumber = (short) lineNumber;
        }

        private static void rangeCheck(int arg, int max, String name) {
                if (arg < 0 || arg > max)
                        throw new IllegalArgumentException(name + ": " + arg);
        }

        @Override
        public boolean equals(Object o) {
                if (o == this)
                        return true;
                if (!(o instanceof PhoneNumber))
                        return false;
                PhoneNumber pn = (PhoneNumber) o;
                return pn.lineNumber == lineNumber && pn.prefix == prefix
                                && pn.areaCode == areaCode;
        }

        @Override
        public int hashCode() {
                int result = 17;
                result = 31 * result + areaCode;
                result = 31 * result + prefix;
                result = 31 * result + lineNumber;
                return result;
        }

    //Effective Java原有的toString方法
        /*
         * @Override public String toString() { return
         * String.format("(%03d) %03d-%04d", areaCode, prefix, lineNumber); }
         */

        /**
         * 采用Guava实现的toString
         *
         */
        @Override
        public String toString() {
                return Objects.toStringHelper(this)
                                .addValue(String.format("(%03d) %03d-%04d", areaCode, prefix,lineNumber))
                                .add("areaCode", areaCode)
                                .add("prefix", prefix)
                                .add("lineNumber", lineNumber)
                                .toString();
        }

        public static void main(String[] args) {
                Map<PhoneNumber, String> m = new HashMap<PhoneNumber, String>();
                m.put(new PhoneNumber(707, 867, 5309), "Jenny");

                System.out.println(m);
        }
}

输出对比