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In this noncompliant code example, constructors for class Boolean return distinct newly-instantiated objects. Using the reference equality operators in place of value comparisons will yield unexpected results.
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public void exampleEqualOperator(){ Boolean b1 = new Boolean("true"); Boolean b2 = new Boolean("true"); if( b1 == b2; ) // never equal System.out.println("Never printed"); } |
Compliant Solution (new Boolean)
In this compliant solution, the values of autoboxed Boolean variables may be compared using the reference equality operators because the Java language guarantees that the Boolean type is fully memoized. Consequently, these objects are guaranteed to be singletons.
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public void exampleEqualOperator(){ Boolean b1 = true; // Or Boolean.True Boolean b2 = true; // Or Boolean.True if(b1 == b2;) // always equal System.out.println("Will always be printed"); } |
Exceptions
EXP03-EX1 In the unusual case where a program is guaranteed to execute only on a single implementation, it is permissible to depend upon implementation-specific ranges of memoized vulnerabilities.
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<ac:structured-macro ac:name="unmigrated-wiki-markup" ac:schema-version="1" ac:macro-id="d3dfed4fe465ed91-9cdbf743-4db0490a-a00f9e21-5bd19185356ec047f4b690ea"><ac:plain-text-body><![CDATA[ | [[JLS 2005 | AA. Bibliography#JLS 05]] | [§5.1.7, "Boxing Conversion" | http://java.sun.com/docs/books/jls/third_edition/html/conversions.html#5.1.7] | ]]></ac:plain-text-body></ac:structured-macro> |
<ac:structured-macro ac:name="unmigrated-wiki-markup" ac:schema-version="1" ac:macro-id="30220c11823b55d0-32ca3d4e-489141ee-a75287ba-a2d7e3ce55034a3099c2cb1c"><ac:plain-text-body><![CDATA[ | [[Pugh 2009 | AA. Bibliography#Pugh 09]] | Using == to compare objects rather than .equals | ]]></ac:plain-text-body></ac:structured-macro> |
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