Hvordan tjekker jeg om tallet er positivt med en metode i Java?

Java kode 

 /**
  * Heater Class
  */
 public class Heater {
     
     private int temperature;
     private final int maxTemperature = 35;
     private final int minTemperature = -10;
     
     //Constructor
     public Heater() {
         temperature = 0;
     }
     
     public void increaseTemperature(int temperature) {
         int temp = getTemperature();
         this.temperature += temperature;
         
         if (isToHigh()) {
             System.out.println("The temperature can't be increased by " + temperature + " degrees, please try again!");
             System.out.println(); //Empty line!
             this.temperature = temp;
         } else {
             System.out.println("The temperature has been increased by " + temperature + " degrees.");
             System.out.println("The heaters new temperature is " + getTemperature());
             System.out.println(); //Empty line!
         }
     }
     
     public void decreaseTemperature(int temperature) {
         int temp = getTemperature();
         this.temperature -= temperature;
 
         if (isToLow()) {
             System.out.println("The temperature can't be descreased by " + temperature + " degrees, please try again!");
             System.out.println(); //Empty line!
             this.temperature = temp;
         } else {
             System.out.println("The temperature has been decreased by " + temperature + " degrees.");
             System.out.println("The heaters new temperature is " + getTemperature());
             System.out.println(); //Empty line!
         }
     }
     
     public int getTemperature() {
         return temperature;
     }
     
     private boolean isToHigh() {
         if (temperature > maxTemperature) {
             return true;
         } else {
             return false;
         }
     }
 
     private boolean isToLow() {
         if (temperature < minTemperature) {
             return true;
         } else {
             return false;
         }
     }
 }