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PODifferent hashcode but HashMap not working
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copied!<p>I have a class <code>myDemoClass</code> to store name and a class to put in a <code>HashMap</code>. While experimenting with overriding <code>hashCode()</code> method, the <code>HashMap</code> is returning <code>null</code> even if hashcodes are different. Why? I have overridden the <code>hashCode()</code> method so that different objects will have different hashcode even if having the same name value.</p> <pre><code>public class myDemoClass { String name; int value; static int i=1; public String getName() { return name; } public void setName(String name) { this.name = name; } public int hashCode() { //return name.hashCode();//now the hashcode are same return i++;//now the hashcode is different } public boolean equals(Object obj) { myDemoClass m=(myDemoClass)obj; if(obj==this) return true; if(obj instanceof myDemoClass) { return getName().equals(m.getName()); } return false; } } </code></pre> <p></p> <pre><code>public class Hashcodes { myDemoClass m1=new myDemoClass(); myDemoClass m2=new myDemoClass(); HashMap h=new HashMap(); public boolean test() { m1.setName("s"); m2.setName("s"); System.out.println(m1.hashCode()); System.out.println(m2.hashCode()); h.put(m1, "a1"); h.put(m1, "b1"); System.out.println(h.get(m1)); System.out.println(h.get(m2)); System.out.println(h.get(m1)); return true; } public static void main(String args[]) { Hashcodes h=new Hashcodes(); h.test(); } } </code></pre> <p>Output with different hashcode:</p> <pre class="lang-none prettyprint-override"><code>1 2 null null null </code></pre> <p>Output with same hashcode:</p> <pre class="lang-none prettyprint-override"><code>115 115 b1 b1 b1 </code></pre>

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