Java: Use hashCode() inside of equals() for convenience?
equals, hashcode, java
Solution
In general, it's not at all safe to compare the `hashCode` instead of using `equals`. When `equals` returns false, `hashCode` may return the same value, per the contract of `hashCode`.
Problem
Consider the following test case, is it a bad practice to use the `hashCode` method inside of equals as a convenient shortcut? ``` public class Test { public static void main(String[] args){ Test t1 = new Test(1, 2.0, 3, new Integer(4)); Test t2 = new Test(1, 2.0, 3, new Integer(4)); System.out.println(t1.hashCode() + "\r\n"+t2.hashCode()); System.out.println("t1.equals(t2) ? "+ t1.equals(t2)); } private int myInt; private double myDouble; private long myLong; private Integer myIntObj; public Test(int i, double d, long l, Integer intObj ){ this.myInt = i; this.myDouble = d; this.myLong = l; this.myIntObj = intObj; } @Override public boolean equals(Object other) { if(other == null) return false; if (getClass() != other.getClass()) return false; return this.hashCode() == ((Test)other).hashCode();//Convenient shortcut? } @Override public int hashCode() { int hash = 3; hash = 53 * hash + this.myInt; hash = 53 * hash + (int) (Double.doubleToLongBits(this.myDouble) ^ (Double.doubleToLongBits(this.myDouble) >>> 32)); hash = 53 * hash + (int) (this.myLong ^ (this.myLong >>> 32)); hash = 53 * hash + (this.myIntObj != null ? this.myIntObj.hashCode() : 0); return hash; } } ``` Output from main method: ``` 1097562307 1097562307 t1.equals(t2) ? true ```