Convert int to object in Java

I have a problem: I work in an eclipse environment

Sometimes the computer does not give the following conversion:

int a ... 
Object ans = (int) a;

But only this conversion:

int a ...
Object ans = (Integer) a;

I understand why you can convert from object to integer, but why is the original variable - sometimes you can, sometimes you can't convert?

thank you

I attach code that the compiler does not allow me to convert between int variables and objects:

/** @return minimum element */
    public Object minimum(){
        return minimum(this.root);
    }
    public Object minimum(BSTNode node){
        if (node.left != null) return minimum(node.left);
        return node.data;
    }
        /** @return maximum element */  
    public Object maximum(){
        return maximum(this.root);
    }
    public Object maximum(BSTNode node){
        if (node.right != null) return maximum(node.right);
        return node.data;
    }

    public Object findNearestSmall(Object elem) {
        int diff;
        diff = (int)maximum() - (int)minimum();
        if (compare(minimum(),elem) == 0) return elem;
        else return findNearestSmall(elem,this.root,diff);
    }   
    public Object findNearestSmall(Object elem,BSTNode node,int mindiff){
           if(node == null) return (int)elem - mindiff;

           int diff = (int)elem - (int)node.data;

           if(diff > 0 && mindiff > diff) mindiff = diff;
           /* Case 2 : Look for in left subtree */
           if(compare(node.data,elem)>-1)
                   return findNearestSmall(elem,node.left,mindiff);
           else
           /* Case 3 : Look for in right subtree */ 
                   return findNearestSmall(elem,node.right,mindiff);
    }

Solution

Before Java 1.5, you couldn't even do this:

int a;
...
Object x = (Integer) a;

The compiler complains that a is a primitive data type and cannot be cast to an object

Since Java 1.5, Java has introduced the concept of automatic boxing Therefore, the following can be:

int a;
...
Object x = (Integer) a;

Because the compiler knows how to automatically convert from the original int to the boxed type integer; From integer to object, it is not a problem

But what you have to do is:

int a;
...
Object x = (int) a;

It basically tells the compiler to avoid boxing You explicitly tell the compiler to leave a as int and put a reference to the int into the object The compiler is not designed to handle this situation