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POModifying final fields in Java
 

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    <p>Let's start with a simple test case:</p> <pre><code>import java.lang.reflect.Field; public class Test { private final int primitiveInt = 42; private final Integer wrappedInt = 42; private final String stringValue = "42"; public int getPrimitiveInt() { return this.primitiveInt; } public int getWrappedInt() { return this.wrappedInt; } public String getStringValue() { return this.stringValue; } public void changeField(String name, Object value) throws IllegalAccessException, NoSuchFieldException { Field field = Test.class.getDeclaredField(name); field.setAccessible(true); field.set(this, value); System.out.println("reflection: " + name + " = " + field.get(this)); } public static void main(String[] args) throws IllegalAccessException, NoSuchFieldException { Test test = new Test(); test.changeField("primitiveInt", 84); System.out.println("direct: primitiveInt = " + test.getPrimitiveInt()); test.changeField("wrappedInt", 84); System.out.println("direct: wrappedInt = " + test.getWrappedInt()); test.changeField("stringValue", "84"); System.out.println("direct: stringValue = " + test.getStringValue()); } } </code></pre> <p>Anybody care to guess what will be printed as output (shown at the bottom as to not spoil the surprise immediately).</p> <p>The questions are:</p> <ol> <li>Why do primitive and wrapped integer behave differently?</li> <li>Why does reflective vs direct access return different results?</li> <li>The one that plagues me most - why does String behave like primitive <code>int</code> and not like <code>Integer</code>?</li> </ol> <p>Results (java 1.5):</p> <pre><code>reflection: primitiveInt = 84 direct: primitiveInt = 42 reflection: wrappedInt = 84 direct: wrappedInt = 84 reflection: stringValue = 84 direct: stringValue = 42 </code></pre>
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    1. USChssPly76
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    1. CO+1: Nice to read your topic.
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      1. USMartijn Courteaux
    2. COthis may tightly related to the compiler.
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      1. USandy
 

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