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e21cbe82a9
Where possible update Java documentation links to Java 11. Additionally update some other links to use HTTPS.
64 lines
2.8 KiB
XML
64 lines
2.8 KiB
XML
<!DOCTYPE qhelp PUBLIC
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"-//Semmle//qhelp//EN"
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"qhelp.dtd">
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<qhelp>
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<overview>
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<p>Primitive values (for example <code>int</code>, <code>float</code>, <code>boolean</code>)
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all have corresponding reference types known as <em>boxed types</em>
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(for example <code>Integer</code>, <code>Float</code>, <code>Boolean</code>). These boxed types
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can be used when an actual object is required. While they all provide
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constructors that take a primitive value of the appropriate type, it is usually considered
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bad practice to call those constructors directly.</p>
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<p>Each boxed type provides a static <code>valueOf</code> method
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that takes an argument of the appropriate primitive type and returns an object representing
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it. The advantage of calling <code>valueOf</code> over calling a constructor is that it allows for
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some caching of instances. By reusing these cached instances instead of
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constructing new heap objects all the time, a significant amount of garbage collector effort can be saved.</p>
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</overview>
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<recommendation>
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<p>In almost all circumstances, a call of, for example, <code>Integer.valueOf(42)</code> can be
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used instead of <code>new Integer(42)</code>.</p>
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<p>Note that sometimes you can rely on Java's
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<em>autoboxing</em> feature, which implicitly calls <code>valueOf</code>. For details, see the
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example.</p>
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</recommendation>
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<example>
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<p>The following example shows the three ways of creating a new integer. In the autoboxing example,
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the zero is autoboxed to an <code>Integer</code> because the constructor <code>Account</code> takes
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an argument of this type.</p>
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<sample src="InefficientPrimConstructor.java" />
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</example>
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<references>
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<li>
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J. Bloch, <em>Effective Java (second edition)</em>,
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Items 1 and 5.
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Addison-Wesley, 2008.
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</li>
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<li>
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Java API Specification:
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<a href="https://docs.oracle.com/en/java/javase/11/docs/api/java.base/java/lang/Boolean.html#valueOf(boolean)">Boolean.valueOf()</a>,
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<a href="https://docs.oracle.com/en/java/javase/11/docs/api/java.base/java/lang/Byte.html#valueOf(byte)">Byte.valueOf()</a>,
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<a href="https://docs.oracle.com/en/java/javase/11/docs/api/java.base/java/lang/Short.html#valueOf(short)">Short.valueOf()</a>,
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<a href="https://docs.oracle.com/en/java/javase/11/docs/api/java.base/java/lang/Character.html#valueOf(char)">Character.valueOf()</a>,
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<a href="https://docs.oracle.com/en/java/javase/11/docs/api/java.base/java/lang/Integer.html#valueOf(int)">Integer.valueOf()</a>,
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<a href="https://docs.oracle.com/en/java/javase/11/docs/api/java.base/java/lang/Long.html#valueOf(long)">Long.valueOf()</a>,
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<a href="https://docs.oracle.com/en/java/javase/11/docs/api/java.base/java/lang/Float.html#valueOf(float)">Float.valueOf()</a>,
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<a href="https://docs.oracle.com/en/java/javase/11/docs/api/java.base/java/lang/Double.html#valueOf(double)">Double.valueOf()</a>.
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</li>
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</references>
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</qhelp>
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