Intent intent = new Intent();  
     intent.putExtra("one", num1);  
     intent.putExtra("str", str);  
     intent.setClass(FirstActivity.this, SecondActivity.class);
     startActivity(intent);

     Intent intent = getIntent(); 
     int num = intent.getIntExtra("one", -1); 
     String string = intent.getStringExtra("str");
 

    Bundle bundle = new Bundle();
    bundle.putString("str", str);
    bundle.putInt("one", num);
    Intent intent = new Intent();
    intent.putExtras(bundle);
    intent.setClass(FirstActivity.this, SecondActivity.class);
    startActivity(intent);
 

    Bundle bundle = getIntent().getExtras(); 
    String str = bundle.getString("str"); 
    int num = bundle.getInt("one");

Intent in=new Intent(); 
in.setClass(Login.this,Regist.class); 
startActivityForResult(in, 1);//requestCode(請求編號)這個編號為有那個頁面跳轉回這個頁面的(因為有可能有多個頁面跳轉到這個頁面A) 
 

Intent in=new Intent(); 
in.setClass(Regist.this, Login.class); 
in.putExtra("username", username); 
in.putExtra("password", password); 
setResult(Activity.RESULT_OK, in); 
finish();

protected void onActivityResult(int requestCode, int resultCode, Intent data) { 
    switch (requestCode) { 
        case 1: 
            String username=data.getStringExtra("username"); 
            String password=data.getStringExtra("password"); 
            usernameEt.setText(username); 
            passwordEt.setText(password); 
            break; 
        default: 
            break; 
    } 
}