六羟甲基三聚氰胺六甲醚。。。给你。
所有的语法错误已经被删除，我已经告诉你的方向，你需要去。

import javax.swing.JOptionPane;

public class VotingData
{

    public static void main(String[] args)
    {
        new VotingData();
    }

    VotingData()
    {

        String[] choices = {"M","F"};
        String[] options = {"a","b"};
        String[] choose = {"Yes","No"};
        String[] decide = {"Trump","Biden"};
        double totalvoters, femalevoters, malevoters, femalebiden, malebiden, femaletrump, maletrump, femalecollegetrump, femalecollegebiden, u25trump, u25biden, totaltrump, totalbiden, totalcollege, totalnoncollege, u25total, over25total;
        totalvoters= femalevoters= malevoters= femalebiden= malebiden= femaletrump= maletrump= femalecollegetrump= femalecollegebiden= u25trump= u25biden= totaltrump= totalbiden= totalcollege= totalnoncollege= u25total= over25total= 0;
        int gender,age,ed,president,stop;

        do
        {
            gender = JOptionPane.showOptionDialog(null, "Select M for male and F for female", "Click a button", JOptionPane.DEFAULT_OPTION,JOptionPane.INFORMATION_MESSAGE, null, choices, choices[0]);
            if(gender==0)
                ++malevoters;
            else
                ++femalevoters;

            age = JOptionPane.showOptionDialog(null, "Select a if you are older than 25 select b if younger", "Click a button", JOptionPane.DEFAULT_OPTION, JOptionPane.INFORMATION_MESSAGE, null, options, options[0]);
            if(age == 0)
                ++over25total;
            else
                ++u25total;

            ed = JOptionPane.showOptionDialog(null, "Select yes if you graduated college, select no if you did not", "Click a button", JOptionPane.DEFAULT_OPTION, JOptionPane.INFORMATION_MESSAGE, null, choose, choose[0]);
            if(ed == 0)
                ++totalcollege;
            else
                ++totalnoncollege;

            president = JOptionPane.showOptionDialog(null, "Select your presidential canidate", "Click a button", JOptionPane.DEFAULT_OPTION, JOptionPane.INFORMATION_MESSAGE, null, decide, decide[0]);
            if(president == 0)
                ++totaltrump;
            else
                ++totalbiden;

            stop = JOptionPane.showOptionDialog(null, "Vote again?", "Click a button", JOptionPane.DEFAULT_OPTION, JOptionPane.INFORMATION_MESSAGE, null, choose, choose[0]);

        }while(stop==0);

        totalvoters=femalevoters+malevoters;
        femalebiden=((totalvoters-malevoters-totaltrump)/totalvoters*100);
        femaletrump=((totalvoters-malevoters-totalbiden)/totalvoters*100);
        malebiden=((totalvoters-femalevoters-totaltrump)/totalvoters*100);
        maletrump=((totalvoters-femalevoters-totalbiden)/totalvoters*100);
        femalecollegebiden=((totalvoters-malevoters-totalnoncollege-totaltrump)/totalvoters*100);
        femalecollegetrump=((totalvoters-malevoters-totalnoncollege-totalbiden)/totalvoters*100);
        u25biden=((totalvoters-over25total-totaltrump)/totalvoters*100);
        u25trump=((totalvoters-over25total-totalbiden)/totalvoters*100);

        int gender1=0;
        while (gender1<20)
        {
            System.out.println(age);
            age++;
            System.out.println("The total number of voters =" + totalvoters);
            System.out.println("The total number of female voters =" + femalevoters);
            System.out.println("The total number of male voters =" + malevoters);
            System.out.println("The total percent of female Biden supporters =" + femalebiden);
            System.out.println("The total percent of female Trump supporters =" + femaletrump);
            System.out.println("The total percent of male Biden supporters =" + malebiden);
            System.out.println("Thetotal percent of male Trump supporters =" + maletrump);
            System.out.println("The total percent of female college educated Bdien supporters =" + femalecollegebiden);
            System.out.println("The total percent of female college edcucated Trump suppoerters =" + femalecollegetrump);
            System.out.println("The total percent of under 25 Biden supporters =" + u25biden);
            System.out.println("The total percent of under 25 Trump supporters =" + u25trump);
            System.out.println("The total amount of voters for Biden =" + totalbiden);
            System.out.println("The total amount of voters for Trump =" + totaltrump);

            System.exit(0);
        }        
    }
}

注意：我没有触及您的计算，也没有更改您的输出代码。我只解决了问题中提到的你的问题。
如果您愿意，请向上投票；）