《Effective Java 第三版》——第九章 通用编程

《Effective Java 第三版》——第二章 创建和销毁对象

《Effective Java 第三版》——第三章 所有对象都通用的方法

《Effective Java 第三版》——第四章 类和接口 

《Effective Java 第三版》——第五章 泛型

 《Effective Java 第三版》——第六章 枚举和注解

 《Effective Java 第三版》——第七章 Lambda 和 Stream 

 《Effective Java 第三版》——第八章 方法

《Effective Java 第三版》——第九章 通用编程

 

package effectivejava.chapter9.item58;
import java.util.*;

// Same bug as NestIteration.java (but different symptom)!! - Page 213
public class DiceRolls {
    enum Face { ONE, TWO, THREE, FOUR, FIVE, SIX }

    public static void main(String[] args) {
        // Same bug, different symptom!
        Collection<Face> faces = EnumSet.allOf(Face.class);

        for (Iterator<Face> i = faces.iterator(); i.hasNext(); )
            for (Iterator<Face> j = faces.iterator(); j.hasNext(); )
                System.out.println(i.next() + " " + j.next());

        System.out.println("***************************");

        for (Face f1 : faces)
            for (Face f2 : faces)
                System.out.println(f1 + " " + f2);
    }
}
/Library/Java/JavaVirtualMachines/jdk-13.0.2.jdk/Contents/Home/bin/java -Dfile.encoding=UTF-8 -classpath /Users/didi/git/effective-java-3e-source-code/bin effectivejava.chapter9.item58.DiceRolls
ONE ONE
TWO TWO
THREE THREE
FOUR FOUR
FIVE FIVE
SIX SIX
***************************
ONE ONE
ONE TWO
ONE THREE
ONE FOUR
ONE FIVE
ONE SIX
TWO ONE
TWO TWO
TWO THREE
TWO FOUR
TWO FIVE
TWO SIX
THREE ONE
THREE TWO
THREE THREE
THREE FOUR
THREE FIVE
THREE SIX
FOUR ONE
FOUR TWO
FOUR THREE
FOUR FOUR
FOUR FIVE
FOUR SIX
FIVE ONE
FIVE TWO
FIVE THREE
FIVE FOUR
FIVE FIVE
FIVE SIX
SIX ONE
SIX TWO
SIX THREE
SIX FOUR
SIX FIVE
SIX SIX

Process finished with exit code 0
package effectivejava.chapter9.item58;

import java.util.*;

public class Card {
    private final Suit suit;
    private final Rank rank;

    // Can you spot the bug?
    enum Suit { CLUB, DIAMOND, HEART, SPADE }
    enum Rank { ACE, DEUCE, THREE, FOUR, FIVE, SIX, SEVEN, EIGHT,
        NINE, TEN, JACK, QUEEN, KING }

    static Collection<Suit> suits = Arrays.asList(Suit.values());
    static Collection<Rank> ranks = Arrays.asList(Rank.values());

    Card(Suit suit, Rank rank ) {
        this.suit = suit;
        this.rank = rank;
    }

    public static void main(String[] args) {
        List<Card> deck = new ArrayList<>();
        
        for (Iterator<Suit> i = suits.iterator(); i.hasNext(); )
            for (Iterator<Rank> j = ranks.iterator(); j.hasNext(); )
                deck.add(new Card(i.next(), j.next()));

//        // Preferred idiom for nested iteration on collections and arrays
//        for (Suit suit : suits)
//            for (Rank rank : ranks)
//                deck.add(new Card(suit, rank));
    }
}
/Library/Java/JavaVirtualMachines/jdk-13.0.2.jdk/Contents/Home/bin/java -Dfile.encoding=UTF-8 -classpath /Users/didi/git/effective-java-3e-source-code/bin effectivejava.chapter9.item58.Card
Exception in thread "main" java.util.NoSuchElementException
    at java.base/java.util.Arrays$ArrayItr.next(Arrays.java:4452)
    at effectivejava.chapter9.item58.Card.main(Card.java:27)

Process finished with exit code 1

 不能遍历同时修改...

package effectivejava.chapter9.item59;

import java.io.IOException;
import java.io.InputStream;
import java.net.URL;

// Printing the contents of a URL with transferTo, added in Java 9 (Page 269)
public class Curl {
    public static void main(String[] args) throws IOException {
        try (InputStream in = new URL(args[0]).openStream()) {
            in.transferTo(System.out);
        }
    }
}
/Library/Java/JavaVirtualMachines/jdk-13.0.2.jdk/Contents/Home/bin/java -Dfile.encoding=UTF-8 -classpath /Users/didi/git/effective-java-3e-source-code/bin effectivejava.chapter9.item59.Curl http://www.baidu.com
<!DOCTYPE html>
<!--STATUS OK--><html> <head><meta http-equiv=content-type content=text/html;charset=utf-8><meta http-equiv=X-UA-Compatible content=IE=Edge><meta content=always name=referrer><link rel=stylesheet type=text/css href=http://s1.bdstatic.com/r/www/cache/bdorz/baidu.min.css><title>百度一下，你就知道</title></head> <body link=#0000cc> <div id=wrapper> <div id=head> <div class=head_wrapper> <div class=s_form> <div class=s_form_wrapper> <div id=lg> <img hidefocus=true src=//www.baidu.com/img/bd_logo1.png width=270 height=129> </div> <form id=form name=f action=//www.baidu.com/s class=fm> <input type=hidden name=bdorz_come value=1> <input type=hidden name=ie value=utf-8> <input type=hidden name=f value=8> <input type=hidden name=rsv_bp value=1> <input type=hidden name=rsv_idx value=1> <input type=hidden name=tn value=baidu><span class="bg s_ipt_wr"><input id=kw name=wd class=s_ipt value maxlength=255 autocomplete=off autofocus></span><span class="bg s_btn_wr"><input type=submit id=su value=百度一下 class="bg s_btn"></span> </form> </div> </div> <div id=u1> <a href=http://news.baidu.com name=tj_trnews class=mnav>新闻</a> <a href=http://www.hao123.com name=tj_trhao123 class=mnav>hao123</a> <a href=http://map.baidu.com name=tj_trmap class=mnav>地图</a> <a href=http://v.baidu.com name=tj_trvideo class=mnav>视频</a> <a href=http://tieba.baidu.com name=tj_trtieba class=mnav>贴吧</a> <noscript> <a href=http://www.baidu.com/bdorz/login.gif?login&amp;tpl=mn&amp;u=http%3A%2F%2Fwww.baidu.com%2f%3fbdorz_come%3d1 name=tj_login class=lb>登录</a> </noscript> <script>document.write('<a href="http://www.baidu.com/bdorz/login.gif?login&tpl=mn&u='+ encodeURIComponent(window.location.href+ (window.location.search === "" ? "?" : "&")+ "bdorz_come=1")+ '" name="tj_login" class="lb">登录</a>');</script> <a href=//www.baidu.com/more/ name=tj_briicon class=bri style="display: block;">更多产品</a> </div> </div> </div> <div id=ftCon> <div id=ftConw> <p id=lh> <a href=http://home.baidu.com>关于百度</a> <a href=http://ir.baidu.com>About Baidu</a> </p> <p id=cp>&copy;2017&nbsp;Baidu&nbsp;<a href=http://www.baidu.com/duty/>使用百度前必读</a>&nbsp; <a href=http://jianyi.baidu.com/ class=cp-feedback>意见反馈</a>&nbsp;京ICP证030173号&nbsp; <img src=//www.baidu.com/img/gs.gif> </p> </div> </div> </div> </body> </html>

Process finished with exit code 0
package effectivejava.chapter9.item59;
import java.util.*;

// Random number generation is hard! - Page 215
public class RandomBug {
    // Common but deeply flawed!
    static Random rnd = new Random();

    static int random(int n) {
        return Math.abs(rnd.nextInt()) % n;
    }

    public static void main(String[] args) {
        int n = 2 * (Integer.MAX_VALUE / 3);
        int low = 0;
        for (int i = 0; i < 1000000; i++)
            if (random(n) < n/2)
                low++;
        System.out.println(low);
    }
}
/Library/Java/JavaVirtualMachines/jdk-13.0.2.jdk/Contents/Home/bin/java -Dfile.encoding=UTF-8 -classpath /Users/didi/git/effective-java-3e-source-code/bin effectivejava.chapter9.item59.RandomBug
666550

Process finished with exit code 0

 

ThreadLocal

package effectivejava.chapter9.item61;

// What does this program do? - Page 274
public class Unbelievable {
    static Integer i;

    public static void main(String[] args) {
        if (i == 42)
            System.out.println("Unbelievable");
    }
}
/Library/Java/JavaVirtualMachines/jdk-13.0.2.jdk/Contents/Home/bin/java -Dfile.encoding=UTF-8 -classpath /Users/didi/git/effective-java-3e-source-code/bin effectivejava.chapter9.item61.Unbelievable
Exception in thread "main" java.lang.NullPointerException
    at effectivejava.chapter9.item61.Unbelievable.main(Unbelievable.java:8)

Process finished with exit code 1

Integer i 在做 == 时自动拆箱，报 NullPointerException 错误





 



 



 



 



 



 













        

	      

	    

	  

	  

	    
      
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          原文地址：https://www.cnblogs.com/cx2016/p/13273238.html