Outputs all possibilities to put + or - or nothing between the numbers 1,2,…,9 (in this order) such that the result is 100.

package defaultpackage;

import javax.script.ScriptEngine;
import javax.script.ScriptEngineManager;
import javax.script.ScriptException;

class Main {
    static int[] pos_counter = {0,0,0,0,0,0,0,0};

    static Boolean running = true;

    public static void main(String[] args) {
        int counter = 0;

        while(running) {
            increment();
            oobcheck();
            try {
                counter = (int) calculate(printeq());
            } catch (ScriptException e2) {
                e2.printStackTrace();
            }
            if(counter==100) {
                System.out.print(printeq());
                System.out.print("=");
                System.out.println(100);
            }
        }
    }

    public static int[] increment(){
        int stepcounter = 7;
        pos_counter[7]++;
        while(stepcounter>= 0&&running){

            if(pos_counter[stepcounter]==3&&running){
                if(stepcounter-1 == -1){
                    running = false;
                } else{
                    pos_counter[stepcounter-1]++;
                    pos_counter[stepcounter]=0;
                }
            }
            stepcounter--;
        }
        return pos_counter;
    }

    public static double calculate(String s) throws ScriptException{
        ScriptEngineManager mgr = new ScriptEngineManager();
        ScriptEngine engine = mgr.getEngineByName("JavaScript");
        return (double) engine.eval(s);
    }

    public static void readout() {
        int stepcounter = 0;
        while(stepcounter <= 7) {
            System.out.print(pos_counter[stepcounter]);
            stepcounter++;
        }
        System.out.println("");
    }

    public static String printeq() {
        int stepcounter = 0;
        String read = "";
        while(stepcounter <= 7) {
            read = "" + read + (stepcounter+1);
            if(pos_counter[stepcounter] == 0){
            }else if(pos_counter[stepcounter] == 1) {
                read = read + "+";
            }else if(pos_counter[stepcounter] == 2) {
                read = read + "-";
            }
            stepcounter++;
        }
        read = read + "9";
        return read;
    }

    public static void oobcheck(){
        int stepcounter = 0;
        Boolean checker = true;
        while(checker&&stepcounter <= 7) {
            if(pos_counter[stepcounter] == 2) {
                stepcounter++;
                checker = true;
            }else{
                checker = false;
            }
            if(stepcounter==7){
                if(pos_counter[7] == 2) {
                    running = false;
                }
            }
        }
    }
}