Coding multiples that equal 100
General Style:

Use functions where you can. You have embedded all the code in to one method.

For many reasons, you should create a function which takes the 100 value as a parameter. Additionally, the purpose of the code is to return pairs of numbers that have 100 as the product, so what you want is a container to store each pair.

This is a start to turning your code in to Object Oriented code.

Classes (OOP)

A container for a result, which is two values that multiply to the target, would be called something like CoFactors (Factors which together make the target). It would look something like:

public class CoFactor {
    private final int lesser, greater;

    public CoFactor(int lesser, int greater) {
        this.lesser = lesser;
        this.greater = greater;
    }

    public int getLesser() {
        return lesser;
    }

    public int getGreater() {
        return greater;
    }
}


Algorithm

Now, with that class, we can return the factors of a number with a method like:

public static final List&lt;CoFactor&gt; getCoFactors(int target) {
    ....
}


The above method will return a list of factors that have the target as a product.

How would that be coded? First, some math....


each factor of a number has a partner (perhaps, if the number is a square number, the partner is itself (3 x 3 = 9 for example) The lesser factor will only be smaller when the lesser factor is less than the square-root of the target....
each small factor has a partnering large factor, and there is only one partner.
we only need to find the small ones to also be able to find the large ones.
we can tell if a number is a factor if there's no remainder after a division (use the % modulo operator)


This can be computed as:

List&lt;CoFactor&gt; factors = new ArrayList&lt;&gt;();
int root = (int)Math.sqrt(target);
for (int attempt = 1; attempt &lt;= root; i++) {
    if (target % attempt == 0) {
        factors.add(new CoFactor(attempt, target / attempt));
    }
}
return factors;