Question

Question 1 (c) (4 marks] For each of the methods equals and hashCode in the following class, explain whether or not they are implemented correctly (with respect to their specification in the object class and any additional specification in this class). If they are not implemented correctly. show how they may be rewritten to address the problems that you have identified. *An immutable representation of a term in a polynomial. " public class Term private int coeff; // the coefficient of the term private int exp; // the exponent of the term ** Creates a new term with coefficient coeff and exponent exp. public Term (int coeff, int exp) this.coeff = coeff; this.exp = exp; /** Returns the coefficient of the term **/ public int get Coeff() { return coeff; /** Returns the exponent of the term **/ public int get Exp() { return exp; + * Returns true if obj is a Term with the same exponent and coefficient as this, and false otherwise. */ @Override public boolean equals (Object obj) ! Term term = (Term) obj; // the Term to compare return ((term.coeff = this.coeff) && (term.exp == this.exp)); @Override public int hashCode) return super.hashCode();

Java Programming.
please give me answer and explain in details.

Answer 1

In first screen shot with output have made changes only in equals method and in second code screen shot i have made changes in both hashcode and equals method please have a look

Output:

2 public class Term{ private int coeff; private int exp; 40 public Term (int coeff, int exp) { this.coeff=coeff; this.exp=exp; } public int getCoeff({ return coeff; } 90 public int getExp() { 10 return exp; } 110 @Override //we can put some more conditions in equals method given by you ..changes made are given below $12 public boolean equals(Object obj){ 13 if(obj==this){ // this condition is to check whether the object refer to the same location like t[@] and t[1] refer to the same object return true; if(!(obj instanceof Term)) { return false; // if we pass any other object other than Term will return false 19 Term term=(Term) obj; return ((term.coeff==this.coeff)&&(term.exp==this.exp)); // here we are checking the value of the object if these values are equal it will return true 21 220 $23 24 @Override public int hashCode() { return super.hashCode(); // we have not make any change in hashcode method It public static void main(String[] args) { Term[] t=new Term[4]; t[0] =new Term(1,2); t[1] =t[@]; // t[@] and t[1] refers to the same location so will give us same hashcode value t[2] =new Term(1,2); t[3] =new Term(3, 4); String str=new String("abc"); System.out.println("checking equals method : "+t[@].equals(t[2]));//here we are checking equals method it should return true but hashcode for both will not be same // because we have not made any change in hashcode method till now. for(int i=0;i<4;i++){ System.out.println("Hashcode for object t["+i+"] : "+t[i].hashCode(); // printing hashcode values for Term objects System.out.println("Hashcode for string object str : "+str.hashcode()); //pcintinh hashcode value for string

Problems @ Javadoc Declaration Console x Debug <terminated Term [Java Application] C:\Program FilesVava\jdk1.8.0_192\bin\javaw.exe (Oct 21, 2019, 3:55:16 PM) checking equals method :true Hashcode for object t[0] : 366712642 Hashcode for object t[1] : 366712642 Hashcode for object t[2] : 1829164700 Hashcode for object t[3] : 2018699554 Hashcode for string object str : 96354

in above output: hascode for t[0] and t[1] is same because they both are referencing to the same object.

hashcode for t[1] and t[2] should be same but its not because we did not made changes in hashcode method  in code of above screenshot.

hashcode of t[3] and string object will be diff because these are different objects

Second screen shot with changes in both equals and hashcode method:

Output:

2 public class Term{ private int coeff; private int exp; 40 public Term (int coeff, int exp) { this.coeff=coeff; this.exp=exp; } public int getCoeff({ return coeff; } 90 public int getExp() { 10 return exp; } 110 @Override //we can put some more conditions in equals method given by you ..changes made are given below $12 public boolean equals(Object obj){ 13 if(obj==this){ // this condition is to check whether the object refer to the same location like t[@] and t[1] refer to the same object return true; if(!(obj instanceof Term)) { return false; // if we pass any other object other than Term will return false 19 Term term=(Term) obj; return ((term.coeff==this.coeff)&&(term.exp==this.exp)); // here we are checking the value of the object if these values are equal it will return true 21 220 223 @Override public int hashCode() { int result= this.coeff * this.exp *999; return result; 25 // after making changes in hashcode method // now for Term object having same values will have same hashcode value 26 270 30 90 mmmmmmmmm public static void main(String[] args) { Term[] t=new Term[4]; t[0] =new Term(1,2); t[1] =t[0]; 1/ t[@] and t[1] refers to the same location so will give us same hashcode value t[2] =new Term(1,2); t[3] =new Term( 3, 4); String str=new String("abc"); System.out.println("checking equals method :"+t[0].equals(t[2]));//here we are checking equals method it should return true and now hashcode for both will be same // because we have made changes in hashcode method now. for(int i=0;i<4; i++){ System.out.println("Hashcode for object t["+i+"] : "+t[i].hashcode()); // printing hashcode values for Term objects System.out.println("Hashcode for string object str : "+str.hashcode()); //printinh hashcode value for string

Problems @ Javadoc Declaration Console X Debug <terminated Term (Java Application) C:\Program Files\Java\jdk1.8.0_192\bin\javaw.exe (Oct 21, 2019, 4:00:33 PM) checking equals method :true Hashcode for object t[0] : 1998 Hashcode for object t[1] : 1998 Hashcode for object t[2] : 1998 Hashcode for object t[3] : 11988 Hashcode for string object str : 96354

Now we can see that the hascode for t[0] and t[1] and t[2] is same as t[0] and t[1] are pointing to the same object and t[1] and t[2] have same values for coeff and exp.

CODE with changes in both method:

public class Term{
   private int coeff;
  
   private int exp;
  
   public Term (int coeff,int exp){
       this.coeff=coeff;
       this.exp=exp;
       }
  
   public int getCoeff(){
       return coeff;
       }
   public int getExp(){
       return exp;
       }
  
   @Override //we can put some more conditions in equals method given by you ..changes made are given below
   public boolean equals(Object obj){
       if(obj==this){ // this condition is to check whether the object refer to the same location like t[0] and t[1] refer to the same object
           return true;
           }
       if(!(obj instanceof Term)){
           return false; // if we pass any other object other than Term will return false
       }
       Term term=(Term) obj;
       return ((term.coeff==this.coeff)&&(term.exp==this.exp)); // here we are checking the value of the object if these values are equal it will return true
   }
  
   @Override
   public int hashCode(){
       int result= this.coeff * this.exp *999; // after making changes in hashcode method
       return result; // now for Term object having same values will have same hashcode value
   }
  
   public static void main(String[] args){
       Term[] t=new Term[4];
       t[0] =new Term(1,2);
       t[1] =t[0]; // t[0] and t[1] refers to the same location so will give us same hashcode value
       t[2] =new Term(1,2);
       t[3] =new Term(3,4);
       String str=new String("abc");
      
       System.out.println("checking equals method :"+t[0].equals(t[2]));//here we are checking equals method it should return true and now hashcode for both will be same
       // because we have made changes in hashcode method now.
       for(int i=0;i<4;i++){
       System.out.println("Hashcode for object t["+i+"] : "+t[i].hashCode()); // printing hashcode values for Term objects
       }
       System.out.println("Hashcode for string object str : "+str.hashCode()); //printinh hashcode value for string
      
   }
}