A simple implementation of the water jug algorithm, works on the principle of repeatedly filling only one jug.

Program.java

package defaultPackage;

public class Program {
  
	public static void main(String args[]) {
		
		WaterJug w = new WaterJug();
		w.checkGoal();
		
		
		
		
	}

}

Waterjug.java

package defaultPackage;
import java.util.*;
public class WaterJug {
  
	int a_max = 2;
	int b_max = 1;
	int a = 0;
	int b = 0;
	int goal = 1;
	
	
	
	void checkGoal() {
		
		int fin = 0;
		
		while(fin != 1) {
			
			if((this.a == this.goal) || (this.b == this.goal)) { fin = 1; }
			
			if(this.a==0) {
				fillA();
				
			} else if ((this.a > 0) && (this.b != this.b_max)) {
				transferAtoB();
				
			} else if ((this.a > 0) && (this.b == this.b_max)) {
				emptyB();
				
			}
			
			
			
			
			
		}
	}
	
	
	void fillA() {
		
		this.a = this.a_max;
		System.out.println("{" + this.a + "," + this.b + "}");
		
	}
	
	void fillB() {
		this.b = this.b_max;
		System.out.println("{" + this.a + "," + this.b + "}");
	}
	
	void transferAtoB() {
		
		int fin = 0;
		
		while(fin != 1) {
			
			this.b += 1;
			this.a -= 1;
			
			if((this.b == this.b_max) || (this.a == 0)) { fin = 1;}

		}
		
		System.out.println("{" + this.a + "," + this.b + "}");
		
	}
	
	void emptyA() {
		
		this.a=0;
		System.out.println("{" + this.a + "," + this.b + "}");
		
	}
	
	void emptyB() {
		this.b=0;
		System.out.println("{" + this.a + "," + this.b + "}");
	}
	
	

}

It is not working when we take a_max=10 , b_max=4 , goal=7. It goes into infinite loop .

because 10m +4b != 7 according to the extended Euclidian Algorithm