2015年5月 – California Sunshine

Google Guava之BiMap

今天介绍一个BiMap的小例子。

import com.google.common.collect.BiMap;
import com.google.common.collect.HashBiMap;
 
 
public class TryBiMap {
 
    public static void main(String[] args) {
        BiMap<String, String> aBiMap = HashBiMap.<String, String>create();
 
        aBiMap.put("abc", "def");
        aBiMap.put("defe", "abcd");
 
        System.out.println(aBiMap); // output: {abc=def, defe=abcd}
        System.out.println(aBiMap.get("abc")); // output: def
 
        // this line will throw a runtime exception
        // because there is "defe":"abcd" already. This record impacts BiMap.inverse.
        // aBiMap.put("abc", "abcd");
 
        // But we can use BiMap.forcePut to put the record of "abc":"abcd"
        // And the record "defe":"abcd" will be erased.
        aBiMap.forcePut("abc", "abcd");
 
        // Use BiMap.inverse() to get a inversed bimap.
        aBiMap = aBiMap.inverse();
 
        System.out.println(aBiMap); // output: {abcd=abc}
        System.out.println(aBiMap.get("abcd")); // output: abc
    }
}

import com.google.common.collect.BiMap;

import com.google.common.collect.HashBiMap;

public class TryBiMap {

public static void main(String[] args) {

BiMap<String, String> aBiMap = HashBiMap.<String, String>create();

aBiMap.put("abc", "def");

aBiMap.put("defe", "abcd");

System.out.println(aBiMap); // output: {abc=def, defe=abcd}

System.out.println(aBiMap.get("abc")); // output: def

// this line will throw a runtime exception

// because there is "defe":"abcd" already. This record impacts BiMap.inverse.

// aBiMap.put("abc", "abcd");

// But we can use BiMap.forcePut to put the record of "abc":"abcd"

// And the record "defe":"abcd" will be erased.

aBiMap.forcePut("abc", "abcd");

// Use BiMap.inverse() to get a inversed bimap.

aBiMap = aBiMap.inverse();

System.out.println(aBiMap); // output: {abcd=abc}

System.out.println(aBiMap.get("abcd")); // output: abc

}

Google Guava之Ordering

Guava提供的Ordering比Comparator强大很多，使用起来非常灵活。下面是个小例子。

import java.util.Arrays;
import java.util.Collections;
import java.util.List;
 
import com.google.common.base.Function;
import com.google.common.collect.Ordering;
 
 
public class TryOrdering {
 
    public static class A implements Comparable<A> {
        int a = 1;
        int b = 2;
 
        public A(int a, int b) {
            this.a = a;
            this.b = b;
        }
 
        public int getA() {
            return this.a;
        }
 
        public int getB() {
            return this.b;
        }
 
        @Override
        public String toString() {
            return String.format("{a=%d,b=%d}", this.a, this.b);
        }
 
        @Override
        public int compareTo(A o) {
            if (this.a > o.a) {
                return 1;
            } else if (this.a < o.b) {
                return -1;
            } else {
                if (this.b > o.b) {
                    return 1;
                } else if (this.b < o.b) {
                    return -1;
                } else {
                    return 0;
                }
            }
        }
    }
 
    enum AFunctions implements Function<A, Integer> {
        GET_A {
 
            @Override
            public Integer apply(A arg0) {
                return arg0.getA();
            }
 
        },
 
        GET_B {
 
            @Override
            public Integer apply(A arg0) {
                return arg0.getB();
            }
 
        }
    }
 
    public static void main(String[] args) {
        Ordering<A> aOrder =
            Ordering.natural()
                .nullsFirst()
                .onResultOf(AFunctions.GET_A)
                .compound(
                        Ordering
                            .natural()
                            .nullsFirst()
                            .onResultOf(AFunctions.GET_B))
                .nullsFirst()
                .reverse();
 
        List<A> as = Arrays.asList(
                        new A(1,2),
                        null,
                        new A(1,3),
                        new A(2,1),
                        new A(2,3),
                        null);
 
        System.out.println(aOrder.isOrdered(as)); // false
 
        Collections.sort(as, aOrder);
        System.out.println(as); // [{a=2,b=3}, {a=2,b=1}, {a=1,b=3}, {a=1,b=2}, null, null]
 
        System.out.println(aOrder.isOrdered(as)); // true
 
        A minA = Collections.min(as, aOrder);
        System.out.println(minA); // {a=2,b=3}
 
        A maxA = Collections.max(as, aOrder);
        System.out.println(maxA); // null
 
        List<A> subAList = aOrder.leastOf(as, 3);
        System.out.println(subAList); // [{a=2,b=3}, {a=2,b=1}, {a=1,b=3}]
    }
 
}

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import java.util.Arrays;

import java.util.Collections;

import java.util.List;

import com.google.common.base.Function;

import com.google.common.collect.Ordering;

public class TryOrdering {

public static class A implements Comparable<A> {

int a = 1;

int b = 2;

public A(int a, int b) {

this.a = a;

this.b = b;

}

public int getA() {

return this.a;

}

public int getB() {

return this.b;

}

@Override

public String toString() {

return String.format("{a=%d,b=%d}", this.a, this.b);

}

@Override

public int compareTo(A o) {

if (this.a > o.a) {

return 1;

} else if (this.a < o.b) {

return -1;

} else {

if (this.b > o.b) {

return 1;

} else if (this.b < o.b) {

return -1;

} else {

return 0;

}

enum AFunctions implements Function<A, Integer> {

GET_A {

@Override

public Integer apply(A arg0) {

return arg0.getA();

}

GET_B {

@Override

public Integer apply(A arg0) {

return arg0.getB();

}

public static void main(String[] args) {

Ordering<A> aOrder =

Ordering.natural()

.nullsFirst()

.onResultOf(AFunctions.GET_A)

.compound(

Ordering

.natural()

.nullsFirst()

.onResultOf(AFunctions.GET_B))

.nullsFirst()

.reverse();

List<A> as = Arrays.asList(

new A(1,2),

null,

new A(1,3),

new A(2,1),

new A(2,3),

null);

System.out.println(aOrder.isOrdered(as)); // false

Collections.sort(as, aOrder);

System.out.println(as); // [{a=2,b=3}, {a=2,b=1}, {a=1,b=3}, {a=1,b=2}, null, null]

System.out.println(aOrder.isOrdered(as)); // true

A minA = Collections.min(as, aOrder);

System.out.println(minA); // {a=2,b=3}

A maxA = Collections.max(as, aOrder);

System.out.println(maxA); // null

List<A> subAList = aOrder.leastOf(as, 3);

System.out.println(subAList); // [{a=2,b=3}, {a=2,b=1}, {a=1,b=3}]

}

小试HTML SVG

因为D3js，最近学习了一下HTML SVG（Scalable Vector Graphics），这里有几个小例子。
[xyz-ihs snippet=”svg-sample”]

[xyz-ihs snippet=”svg-sample-2″]

老生常谈：绝不要拷贝代码！！

首先要说一句老话，拷贝是万恶之源，是最差实践之首。

前段时间，组里有个同事实现某个新功能，其实挺简单的，前后大约做了两周。最后在Code Review的时候，发现有很多没调用到的方法和变量，代码逻辑很奇怪，然后发现代码是从另一处Copy过来的，只是稍作加工。再然后，我就让另一名工程师加入一起清理代码，又花了4天才把逻辑理清楚。清理之后的代码比之前少了60~70%，更易于维护。这一切都是Copy Code惹的祸。

为什么拷贝代码？

省工夫省时间？

Copy/Paste, so fast! 这是非常非常短视的想法，甚至有时连短期的工夫和时间都没有节省到。因为老代码里有大量逻辑，不一定拷贝过去可以直接使用。这时必然Bug漫天飞，怎么能过的了QA那关。长远看就更加不可取，无数血泪的经验，大量重复代码是项目的灾难，不可能有好的设计，后期维护的工程师会叫苦连天，工期不断延后，质量只能是垃圾，不要期盼有什么保证。垃圾的代码也留不住好的程序员，学不到任何东西，他们的青春为什么拿来给别人擦屁股。

时间和工夫有时不能省的，要耐着性子看老代码里的逻辑，”慢就是快“。

”某种项目需要“！

还有另一种可能-项目需要！一些稍大的公司或组织会同时进行几个项目，新的项目可能会在老项目的代码上扩展。为了节省工期，有些Team就直接把老项目的代码在新项目的Branch上拷贝一份。开始一切很祥和，可新老项目同时继续，同时在修Bug，加Feature。时间长了，就有可能在不同的代码Branch做Merge，也是要花大量的时间和精力。究其根源有很多，可能真是工期紧，可能是老代码的设计太差。

我觉得设计的问题大一些。这不是理想的做法，应该把需要依赖的代码做提取，对于不同行为做抽象，再以注入等方式改变所依赖代码的行为。

如何避免代码里的Duplication？

做为工程师应该了解，Code不单是为别人写的，也是给未来的自己写的。不想六个月之后砸键盘吧！时刻牢记”Duplication is evil!”
做好培训，尤其是新手。大多新手带着从学校实验室的“恶习”（想想那些教授老板也被坑的不轻，还不自知），入职后老员工的”传帮带“很重要。
鼓励做代码重构，罗马不是一天建成的，代码也不是一天就能变好。
制定Team里的Coding Guideline，加强Code Review。大家都知道”破窗理论“，有规则才能遵守，不然只能越来越糟。
组织里要有分享代码的意识，多做独立于产品的可复用的代码模块。假以时日就可形成客观的代码“资产”，大大加速日后的开发和团队效率。
使用SonarQube实时掌握重复代码的情况。SonarQube是个非常强大的工具，帮助团队实时的监控代码质量的变化，Duplication就是其中的一个维度。

总结

不要拷贝代码。That’s it!

Google Guava之Table

这个小例子介绍如何使用Guava提供的Table类。

import com.google.common.collect.HashBasedTable;
import com.google.common.collect.Table;
 
 
public class TryTable {
 
    public static void main(String[] args) {
 
        Table<String, String, String> aTable = HashBasedTable.create();
 
        // create a table;
        for (char a = 'A'; a <= 'C'; ++a) {
            for (char b = '1'; b <= '3'; ++b) {
                // put()
                // first is rowKey, second is columnKey, third is the value.
                aTable.put(Character.toString(a), Character.toString(b), String.format("%c%c", a, b));
            }
        }
 
        // query a specific column
        System.out.println(aTable.column("2")); // {A=A2, B=B2, C=C2}
 
        // query a specific row
        System.out.println(aTable.row("B")); // {3=B3, 2=B2, 1=B1}
 
        // query a cell
        System.out.println(aTable.get("B", "2")); // B2
 
        // contains test
        System.out.println(aTable.contains("D", "1")); // false
        System.out.println(aTable.containsColumn("3")); // true
        System.out.println(aTable.containsRow("C"));  // true
 
        System.out.println(aTable.columnMap()); // {3={A=A3, B=B3, C=C3}, 2={A=A2, B=B2, C=C2}, 1={A=A1, B=B1, C=C1}}
        System.out.println(aTable.rowMap()); // {A={3=A3, 2=A2, 1=A1}, B={3=B3, 2=B2, 1=B1}, C={3=C3, 2=C2, 1=C1}}
 
        // Remove a cell
        System.out.println(aTable.remove("B", "3")); // B3
    }
 
}

import com.google.common.collect.HashBasedTable;

import com.google.common.collect.Table;

public class TryTable {

public static void main(String[] args) {

Table<String, String, String> aTable = HashBasedTable.create();

// create a table;

for (char a = 'A'; a <= 'C'; ++a) {

for (char b = '1'; b <= '3'; ++b) {

// put()

// first is rowKey, second is columnKey, third is the value.

aTable.put(Character.toString(a), Character.toString(b), String.format("%c%c", a, b));

}

// query a specific column

System.out.println(aTable.column("2")); // {A=A2, B=B2, C=C2}

// query a specific row

System.out.println(aTable.row("B")); // {3=B3, 2=B2, 1=B1}

// query a cell

System.out.println(aTable.get("B", "2")); // B2

// contains test

System.out.println(aTable.contains("D", "1")); // false

System.out.println(aTable.containsColumn("3")); // true

System.out.println(aTable.containsRow("C")); // true

System.out.println(aTable.columnMap()); // {3={A=A3, B=B3, C=C3}, 2={A=A2, B=B2, C=C2}, 1={A=A1, B=B1, C=C1}}

System.out.println(aTable.rowMap()); // {A={3=A3, 2=A2, 1=A1}, B={3=B3, 2=B2, 1=B1}, C={3=C3, 2=C2, 1=C1}}

// Remove a cell

System.out.println(aTable.remove("B", "3")); // B3

}

Google Guava之Objects

Guava Objects是个非常好用的类，帮助我们写出hashCode(), equals()和toString()。

看下面的小例子。

public class TryObjects {
 
    private int i;
    private Double d;
 
    /**
     * Default ctor.
     */
    public TryObjects() {
        this(10, 1.0);
    }
 
    /**
     * Ctor with i and d.
     * @param i i
     * @param d d
     */
    public TryObjects(int i, double d) {
        this(i, d);
    }
 
    @Override
    public boolean equals(Object arg0) {
        if (arg0 == null || !(arg0 instanceof TryObjects)) {
            return false;
        } else {
            TryObjects obj = (TryObjects)arg0;
            return Objects.equal(this.i, obj.i)
                && Objects.equal(this.d, obj.d); // 不用担心null的情况
        }
    }
 
    @Override
    public int hashCode() {
        return Objects.hashCode(this.i, this.d);
    }

    @Override
    public String toString() {
        // TryObjects{i=10, d=1.0}
        return Objects.toStringHelper(TryObjects.class)
                .add("i", this.i)
                .add("d", this.d)
                .toString();
    }
}

public class TryObjects {

private int i;

private Double d;

/**

* Default ctor.

public TryObjects() {

this(10, 1.0);

}

/**

* Ctor with i and d.

* @param i i

* @param d d

public TryObjects(int i, double d) {

this(i, d);

}

@Override

public boolean equals(Object arg0) {

if (arg0 == null || !(arg0 instanceof TryObjects)) {

return false;

} else {

TryObjects obj = (TryObjects)arg0;

return Objects.equal(this.i, obj.i)

&& Objects.equal(this.d, obj.d); // 不用担心null的情况

}

@Override

public int hashCode() {

return Objects.hashCode(this.i, this.d);

}

@Override

public String toString() {

// TryObjects{i=10, d=1.0}

return Objects.toStringHelper(TryObjects.class)

.add("i", this.i)

.add("d", this.d)

.toString();

}

C41彩色负片摄影

自从成功D76黑白胶片冲洗之后，就对彩色胶片跃跃欲试。对比黑白胶片，C41彩色负片的冲洗要复杂的多，步骤多，尤其要控制在显影（Develop）阶段（约3分30秒）的温度。在长时间的准备后，试着自己冲洗了几卷Kodak Professional Portra 400 Color Negative Film。第一卷比较失败，色偏的厉害，慢慢掌握之后，后面几卷还不错，放几张上来让大家看看效果吧。之后，我会做个完整的教程。

How to specify the configuration file when starting mysqld?

In our development machine, I don’t have the root permission to install MySQL server. But our SonarQube needs it.

Fortunately, if you using the MySQL TAR archive, “root” is not required to launch mysqld but you need specify the configuration file. The default one uses some folders which need root to access.

Here is the sample mysqld configuration. You can also start from a configuration file in folder support-files.

# For advice on how to change settings please see
# http://dev.mysql.com/doc/refman/5.6/en/server-configuration-defaults.html

[mysqld]
user=yli

# Remove leading # and set to the amount of RAM for the most important data
# cache in MySQL. Start at 70% of total RAM for dedicated server, else 10%.
# innodb_buffer_pool_size = 128M

# Remove leading # to turn on a very important data integrity option: logging
# changes to the binary log between backups.
# log_bin

# These are commonly set, remove the # and set as required.
basedir = /home/yli/mysql-5.6.16-linux-glibc2.5-x86_64
datadir = /home/yli/sonar_mysql_db
# port = .....
# server_id = .....
# socket = .....

# Remove leading # to set options mainly useful for reporting servers.
# The server defaults are faster for transactions and fast SELECTs.
# Adjust sizes as needed, experiment to find the optimal values.
# join_buffer_size = 128M
# sort_buffer_size = 2M
# read_rnd_buffer_size = 2M 

sql_mode=NO_ENGINE_SUBSTITUTION,STRICT_TRANS_TABLES

# For advice on how to change settings please see

# http://dev.mysql.com/doc/refman/5.6/en/server-configuration-defaults.html

[mysqld]

user=yli

# Remove leading # and set to the amount of RAM for the most important data

# cache in MySQL. Start at 70% of total RAM for dedicated server, else 10%.

# innodb_buffer_pool_size = 128M

# Remove leading # to turn on a very important data integrity option: logging

# changes to the binary log between backups.

# log_bin

# These are commonly set, remove the # and set as required.

basedir = /home/yli/mysql-5.6.16-linux-glibc2.5-x86_64

datadir = /home/yli/sonar_mysql_db

# port = .....

# server_id = .....

# socket = .....

# Remove leading # to set options mainly useful for reporting servers.

# The server defaults are faster for transactions and fast SELECTs.

# Adjust sizes as needed, experiment to find the optimal values.

# join_buffer_size = 128M

# sort_buffer_size = 2M

# read_rnd_buffer_size = 2M

sql_mode=NO_ENGINE_SUBSTITUTION,STRICT_TRANS_TABLES

Basically, you need specify the basedir and datadir to tell mysql where it’s installed and where the database files should be put.

Other settings can keep the same as defaults in my case. Then I start the server instance. Option “–defaults-file” is important.

[yli@my_laptop ~/mysql-5.6.16-linux-glibc2.5-x86_64]$ bin/mysqld --defaults-file=/home/yli/mysql-5.6.16-linux-glibc2.5-x86_64/my.cnf

1	[yli@my_laptop ~/mysql-5.6.16-linux-glibc2.5-x86_64]$ bin/mysqld --defaults-file=/home/yli/mysql-5.6.16-linux-glibc2.5-x86_64/my.cnf

References

How to find configuration file MySQL uses?

读《最后期限》

一本挺有意思的老书！作者把项目管理的知识融入了一个离奇的、不可能在现实世界发生的项目（或者叫实验或冒险），最后再加上一个完美的英雄美人式的大结局，让我等IT男屌丝情何以堪啊。这Project Manager也太美了吧，”财色兼收“啊！

故事之外，有些道理挺好，摘几句有感触的。

度量每个产品的规模，运用各种工具和方法做好估算。
压力之下人无法快速思考。短期的压力对团队可能是有益的，帮助团队成员集中注意，但长期的压力一定是错误的。（深有感触！）
生产力提高来自长期的投资，平时要加强团队学习和建设。（罗马不是一天建成的）
除非必要，否则不要自己去凝聚一个团队：出去找已经成型的团队。（这就是为什么要挖挖一窝吧）
项目开始的浪费一天和Deadline之前浪费的一天，它们的危害是相同的。（珍惜时间）
组织里时常有“神经”的人，提一些不可能的需求，如不可能的deadline. 你不能满足所有Stakeholder的需求，要寻求影响力更大人的帮助，再不然，可以考虑走人了。别想根治一个神经的人。（主人公的做法在现实中是不可取的。）
不要辱骂团队成员，没人能在辱骂之后表现的更好。
拒绝含糊的规格文档。（实现和其他产品一样的功能！OMG）
适当的处理团队中的冲突。
项目需要仪式！

Set of P4 Command Alias

VirtualBox果然还是不及VMware，越用越慢，让人崩溃啊。现在公司又不让自己装软件了（正版也不行），只好另辟蹊径。好在Java可以跨平台，于是便在Window 7里新搭了开发环境，在Window下写代码和Unit Test，去Linux下编译验证，代码通过P4 Shelve传递。几次下来，发现P4 Command挺方便，总结几个Alias和大家分享。 😆

# Used in tcsh
alias ppc p4 changes -s pending -c $P4CLIENT
alias prc p4 revert -c \!:1 //...
alias puf p4 unshelve -s \!:1 -c \!:2 -f //...
alias pdc p4 change -d \!:1
alias pc  p4 change
alias psfg p4 sync -f //xx/yy/zz/...
alias psg p4 sync //xx/yy/zz/...
alias pdec p4 describe \!:1

# Used in tcsh

alias ppc p4 changes -s pending -c $P4CLIENT

alias prc p4 revert -c \!:1 //...

alias puf p4 unshelve -s \!:1 -c \!:2 -f //...

alias pdc p4 change -d \!:1

alias pc p4 change

alias psfg p4 sync -f //xx/yy/zz/...

alias psg p4 sync //xx/yy/zz/...

alias pdec p4 describe \!:1