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POInfinite loops in Java
 

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    <p>Look at the following infinite <code>while</code> loop in Java. It causes a compile-time error for the statement below it.</p> <pre><code>while(true) { System.out.println("inside while"); } System.out.println("while terminated"); //Unreachable statement - compiler-error. </code></pre> <hr> <p>The following same infinite <code>while</code> loop, however works fine and doesn't issue any errors in which I just replaced the condition with a boolean variable.</p> <pre><code>boolean b=true; while(b) { System.out.println("inside while"); } System.out.println("while terminated"); //No error here. </code></pre> <hr> <p>In the second case also, the statement after the loop is obviously unreachable because the boolean variable <code>b</code> is true still the compiler doesn't complain at all. Why?</p> <hr> <p><strong>Edit :</strong> The following version of <code>while</code> gets stuck into an infinite loop as obvious but issues no compiler errors for the statement below it even though the <code>if</code> condition within the loop is always <code>false</code> and consequently, the loop can never return and can be determined by the compiler at the compile-time itself.</p> <pre><code>while(true) { if(false) { break; } System.out.println("inside while"); } System.out.println("while terminated"); //No error here. </code></pre> <hr> <pre><code>while(true) { if(false) { //if true then also return; //Replacing return with break fixes the following error. } System.out.println("inside while"); } System.out.println("while terminated"); //Compiler-error - unreachable statement. </code></pre> <hr> <pre><code>while(true) { if(true) { System.out.println("inside if"); return; } System.out.println("inside while"); //No error here. } System.out.println("while terminated"); //Compiler-error - unreachable statement. </code></pre> <hr> <p><strong>Edit :</strong> Same thing with <code>if</code> and <code>while</code>.</p> <pre><code>if(false) { System.out.println("inside if"); //No error here. } </code></pre> <hr> <pre><code>while(false) { System.out.println("inside while"); // Compiler's complain - unreachable statement. } </code></pre> <hr> <pre><code>while(true) { if(true) { System.out.println("inside if"); break; } System.out.println("inside while"); //No error here. } </code></pre> <hr> <p>The following version of <code>while</code> also gets stuck into an infinite loop.</p> <pre><code>while(true) { try { System.out.println("inside while"); return; //Replacing return with break makes no difference here. } finally { continue; } } </code></pre> <p>This is because the <code>finally</code> block is always executed even though the <code>return</code> statement encounters before it within the <code>try</code> block itself.</p>
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    1. COWho cares? It's obviously just a feature of the compiler. Don't concern yourself with this sort of stuff.
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    2. COHow could another thread change a local non-static variable?
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    3. COThe internal state of the object might be changed concurrently through reflection. That's why the JLS mandates that only final (constant) expressions be checked.
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