public class login {
 private String username;
 private String password;

public String getUsername() {
    return username;
}
public void setUsername(String username) {
    this.username = this.usernameTextField.getText();
}
public String getPassword() {
    return password;
}
public void setPassword(String password) {
    this.password = this.passwordTextField.getText();
}
}

private void jButton3ActionPerformed(java.awt.event.ActionEvent evt) {
      String msg= tx.getText();
      new NewJFrame2(msg).setVisible(true);
    }

public NewJFrame2(String abc ){
        initComponents();
        lx.setText(abc);
    }

The 100% working sollution
-----------------------------

for login.java
----------------
suppose u r calling welcome.java:
Account ac= new Account(new JFrame(), true);
after this line call a method of welcome.java which u have to create like:
wc.setUser(username);

for account.java
------------------

create a method:void setUser(String username) {
        user1 = user;
        cname.setText(user1);
    }

user1 is global variable and available for all which u have to define lke:
String user1;
after it is assigning the username value to user1
here cname is a label which name is cname;
so, we are seeting the text of cname to the user.