if else statement dont work on button activity

i have an login screen where i have a username. if the username is "z" my programe shpould go in the if statement but it always goes in the else. i try always to write z on username but he is always sending me fail. where is the fault ? i mean before the statement i have some system outs who give out the correct strings in the username edittext...

    import android.os.Bundle;
        import android.support.v4.app.FragmentActivity;
        import android.view.View;
        import android.widget.Button;
        import android.widget.EditText;

public class MainActivity extends FragmentActivity {
    // Fragment TabHost as mTabHost
    EditText text;
    Button login;
    EditText password;
    String username;
    @Override
    protected void onCreate(Bundle savedInstanceState) {

        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        text = (EditText) findViewById(R.id.editText);
        login = (Button) findViewById(R.id.button);
        password = (EditText) findViewById(R.id.editText2);


        login.setOnClickListener(new View.OnClickListener(){
            public void onClick(View view){
                username =text.getText().toString();
                System.out.println(text.getText().toString());
                System.out.println(password.getText().toString());

                if(username =="z"  ){
                    System.out.println("success");
                }else{
                    System.out.println("Fail");
                }

            }

        });


    }


}