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<div align="center" class="title">JAVA程序員必讀：基礎篇（4）對象和簡單數據對象</div>
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<div align="center"><font color="#666666">編譯：ZSC/太平洋網絡學院</font></div>
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<div align="right" class="gray"><a href="mailto:tntst@pconline.com.cn">［責編:爆破手］</a></div>
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<p class="article"><b>對象和簡單數據對象</b></p>
<p class="article"><b>（6）將String轉換為數字</b></p>
<p class="article"> String類本身沒有提供任何的方法來轉換String為浮點型、整型或者其它的數值類型。但是，"type
wrapper"類的四種類型（integer、Double、Float和Long）提供了一個類方法valueOf來將String轉換為那個類型的對象。舉例如下：
</p>
<p class="article">String piStr = "3.14159";</p>
<p class="article">Float pi = Float.valueOf(piStr);</p>
<p></p>
<p class="article"><b>（7）Strings和JAVA編譯器</b></p>
<p class="article"> JAVA編譯器使用了String和StringBuffer類來處理字符串和字符串的連接。</p>
<p class="article">下面先講講Strings：</p>
<p class="article">在JAVA種，你可以在雙引號之間指定字符串，如： </p>
<p class="article">"Hello World!"</p>
<p class="article"> 你可以在任何使用String對象的地方使用字符串。比如，System.out.println接收一個String參數，所以你可以在這里使用字符串了。</p>
<p class="article">System.out.println("Might I add that you look lovely
today.");</p>
<p class="article"> 同樣，你可以使用從字符串直接使用String方法，比如： </p>
<p class="article">int len = "Goodbye Cruel World".length();</p>
<p class="article"> 因為編譯器自動為字符串創建了一個新的String對象，你可以使用字符串來初始化一個String對象：
</p>
<p class="article">String s = "Hola Mundo";</p>
<p class="article">上面的這條語句等價于下面的語句： </p>
<p class="article">String s = new String("Hola Mundo");</p>
<p class="article"> 最后講講字符串的連接以及+運算符：</p>
<p class="article"> 在JAVA種，你可以使用+來連接字符串，比如： </p>
<p class="article">String cat = "cat";</p>
<p class="article">System.out.println("con" + cat + "enation");</p>
<p class="article"> 這條語句看起來有點問題，因為我們直到Strings是不能改變的。但是，在這條語句的背后，編譯器卻使用了StringBuffers來執行字符串的連接。上面的語句實際上編譯為：
</p>
<p class="article">String cat = "cat";</p>
<p class="article">System.out.println(new StringBuffer().append("con").</p>
<p class="article"> append(cat).append("enation").toString());</p>
<p class="article"> 同樣你可以使用+運算符號來增不一個String： </p>
<p class="article">System.out.println("Java's Number " + 1);</p>
<p class="article"> 在JAVA中，在執行字符串連接操作之前編譯器講非String的數值（如本例的整數1）轉化為一個String對象。</p>
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