How to generate multiple nested repeat structures with methods

I need to generate multiple nested structures (26) I wanted to know how to do this with pro code methods do not get too large an example of the structure I need with 4 nested:

public static void main(String[] args) {
    String[] vet={"1","2","3","4"};
    for(int i=0;i<4;i++)
        for(int j=0;j<4;j++) if(i!=j)
            for(int k=0;k<4;k++) if(j!=k && i!=k)
                for(int l=0;l<4;l++) if(k!=l && i!=l && j!=l)
                    System.out.println(vet[i]+vet[j]+vet[k]+vet[l]);

}