为什么for循环得不到返回值？

输出结果是这样的，为什么gallonNeed的值没带回来？

Please input the length of the room>>

15

Please input the width of the room>>

20

Please input the height of the room>>

10

0

This room needs 0gallons

the whole payment is $0

package chapter3;

import java.util.Scanner;

public class PaintCalculator {

public static void main(String[] args) {

// TODO Auto-generated method stub

Scanner input=new Scanner(System.in);

System.out.println("Please input the length of the room>>");

int length=input.nextInt();

System.out.println("Please input the width of the room>>");

int width=input.nextInt();

System.out.println("Please input the height of the room>>");

int height=input.nextInt();

int area=wallArea(length, width, height);

int gallonNeed=gallonNeed(area);

displayGallonNeed(gallonNeed);

displayPayment(gallonNeed);

}

public static int wallArea(int length, int width, int height) {

int area=2*(length*height+width*height)+length*width;

return area;

}

public static int gallonNeed(int area) {

int gallonNeed=0;

for(int n=0;area>=(350*n)&&area<=(350*(n+1));n++) {

gallonNeed=n;

}

System.out.println(gallonNeed);

return gallonNeed;

}

public static void displayGallonNeed(int gallonNeed) {

System.out.println("This room needs "+gallonNeed+"gallons");

}

public static void displayPayment(int gallonNeed) {

int payment=gallonNeed*32;

System.out.println("the whole payment is $"+payment);

}

}