新建一个FirstActivity ：

public class FirstActivity extends AppCompatActivity {

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.first_layout);
        Button but1 = (Button) findViewById(R.id.but1);
        but1.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {

#显示intent，向SecondActivity传递数据

                Intent intent = new Intent(FirstActivity.this,SecondActivity.class);
                String data = "testtest";#比如传递string类数据
                intent.putExtra("first_input",data);#相当于key为first_input，value为data 
                startActivityForResult(intent,1);#1表示request_code可以为任意的确定值
            }
        });
    }

#返回值处理函数，可以先看下面的SecondActivity
@Override
    protected void onActivityResult(int requestCode, int resultCode, Intent data)
 {#第一个参数为上面startActivityForResult中所填的request_code，第二个参数resultCode为后面另一个activity（SecondActivity）的函数中设置的返回code，data为SecondActivity中返回的数据
        switch (requestCode){
            case 1:
                if(resultCode == RESULT_OK){
                    String da = data.getStringExtra("feedback");
                    Log.d("FirstActivity",da);
                }
        }

    }

第一个activity对应xml：

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:orientation="vertical" android:layout_width="match_parent"
    android:layout_height="match_parent">
<Button android:id="@+id/but1"
    android:layout_height="wrap_content"
    android:layout_width="match_parent"
    android:text="click"
    />

</LinearLayout>

现在另建一个SecondActivity:

public class SecondActivity extends AppCompatActivity {

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_second);
        Button button = (Button) findViewById(R.id.but_2);

        Intent intent = getIntent(); #获取FirstActivity 传递的intent
        String a = intent.getStringExtra("first_input"); #取得key为first_input的值value

        Log.d("SecondActivity",a);
        button.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                Intent intent = new Intent(); #新建显式的intent
                intent.putExtra("feedback","feedback info"); #把返回值对应key，value存入intent
                setResult(RESULT_OK,intent); #通过setResult函数把intent返回给firstactivity，参数1一般有默认值RESULT_OK，RESULT_CANCELLED等
                finish(); #完成后销毁activity2

            }
        });
    }
}

对应xml：

<?xml version="1.0" encoding="utf-8"?>
<android.support.constraint.ConstraintLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    tools:context="com.example.javascript.activitytest.SecondActivity">
<Button
    android:layout_width="match_parent"
    android:layout_height="wrap_content"
    android:text="but2"
    android:id="@+id/but_2"/>
</android.support.constraint.ConstraintLayout>