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copied!<p>"" is an actual string, albeit an empty one.</p> <p>null, however, means that the String variable points to nothing.</p> <p><code>a==b</code> returns false because "" and null do not occupy the same space in memory--in other words, their variables don't point to the same objects.</p> <p><code>a.equals(b)</code> returns false because "" does not equal null, obviously.</p> <p>The difference is though that since "" is an actual string, you can still invoke methods or functions on it like</p> <p><code>a.length()</code></p> <p><code>a.substring(0, 1)</code></p> <p>and so on.</p> <p>If the String equals null, like b, Java would throw a <code>NullPointerException</code> if you tried invoking, say:</p> <p><code>b.length()</code></p> <hr> <p>If the difference you are wondering about is == versus equals, it's this: </p> <p>== compares references, like if I went</p> <pre><code>String a = new String(""); String b = new String(""); System.out.println(a==b); </code></pre> <p>That would output false because I allocated two different objects, and a and b point to different objects.</p> <p>However, <code>a.equals(b)</code> in this case would return true, because <code>equals</code> for Strings will return true <a href="http://docs.oracle.com/javase/7/docs/api/java/lang/String.html#equals(java.lang.Object)">if and only if the argument String is not null and represents the same sequence of characters.</a></p> <p>Be warned, though, that Java does have a special case for Strings.</p> <pre><code>String a = "abc"; String b = "abc"; System.out.println(a==b); </code></pre> <p>You would think that the output would be <code>false</code>, since it should allocate two different Strings. Actually, Java will <a href="http://docs.oracle.com/javase/7/docs/api/java/lang/String.html#intern()">intern</a> literal Strings (ones that are initialized like a and b in our example). So be careful, because that can give some false positives on how == works.</p>

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