java - Receive new value by two Class constructors -

i have 2 class:

public class classa {  string newname;  public classa() {     system.out.println("new name in constructor: " + newname); }  public static void main(string[] args) {     classa = new classa();     am.action();     am.displaynewname(); }  public void displaynewname() {     system.out.println("new name in display method:" + getnewname()); }  public void action() {     classb ba = new classb();     system.out.println("new name in action:" + getnewname()); }  public string getnewname() {     return newname; }  public void setnewname(string newn) {     newname = newn;     system.out.println("new name in set method: " + getnewname()); } } 

and:

public class classb {  string newname = "jack"; classa a;  public classb(){     a.setnewname(newname); } } 

i can not receive jack value on classa methods (like displaynewname() , action methods.

update

    public class classb {  string newname = "jack"; classa = new classa();  public classb(){     a.setnewname(newname); } } 

output:

new name in constructor: null new name in constructor: null new name in set method: jack new name in action:null new name in display method:null 

variable a not initialized. throw nullpointerexception. need initialize in constructor adding line : a = new classa();

edit1:

from understood, need this:

public class classb {  string newname = "jack";  public classb(classa a){     a.setnewname(newname); } } 

and in classb, modify action()

public void action() {     classb ba = new classb(this);     system.out.println("new name in action:" + getnewname()); }