// FUNÇÃO - ENTRAR
    public void call_Entrar(View view) {

        // Validar Internet
        // ...

        // Informar Conexão
        // ...

        // Variáveis
        String host     =   "localhost";
        String port     =   "5432";
        String db       =   "database";
        String user     =   "postgres";
        String pass     =   "postgres";

        // ConexaoMD
        new ConexaoMD(host, port, db, user, pass);

        // ConexaoDAO
        boolean conexao = new ConexaoDAO().conectarPostgreSQL(host, port, db, user, pass);

        AlertDialog alertDialog1 = new AlertDialog.Builder(AcessarActivity.this).create();
        alertDialog1.setTitle("Aviso!");
        alertDialog1.setMessage("Banco de Dados: " + conexao);
        alertDialog1.setButton(AlertDialog.BUTTON_NEUTRAL, "OK", new DialogInterface.OnClickListener() {
            public void onClick(DialogInterface dialog, int which) {
                dialog.dismiss();
            }
        });
        alertDialog1.show();

    }

package model;

// Variáveis

private String host;
private String port;
private String db;
private String user;
private String pass;

// Construtor
public ConexaoMD(String host, String port, String db, String user, String pass) {
    this.host = host;
    this.port = port;
    this.db = db;
    this.user = user;
    this.pass = pass;
}

// Getters & Setters

public String getHost() {
    return host;
}
public void setHost(String host) {
    this.host = host;
}
public String getPort() {
    return port;
}
public void setPort(String port) {
    this.port = port;
}
public String getDb() {
    return db;
}
public void setDb(String db) {
    this.db = db;
}
public String getUser() {
    return user;
}
public void setUser(String user) {
    this.user = user;
}
public String getPass() {
    return pass;
}
public void setPass(String pass) {
    this.pass = pass;
}

package dao;

// Variáveis
private Connection conn = null;
private Statement st;
private ResultSet rs;
private String sql;

// Construtor
public boolean conectarPostgreSQL(String host, String port, String db, String user, String pass){

    try{
        Class.forName("com.postgresql.Driver").newInstance();
        conn=DriverManager.getConnection(
                "jdbc:postgresql://"+host+":"+port+"/"+db+"?connectTimeout=9000&socketTimeout=9000&autoReconnect=true&secondsBeforeRetryMaster=3",user,pass);
        return true;
    } catch(Exception erro){
        Log.e("PostgreSQL","Erro: "+erro);
        return false;
    }

}

public void desconectarPostgreSQL(){
    try{
        conn.close();
        Log.i("PostgreSQL","Desconectado.");
    } catch(Exception erro){
        Log.e("PostgreSQL","Erro: "+erro);
    }
}

public ResultSet queryPostgreSQL(String qry){
    try{
        st = conn.createStatement();
        sql = qry;
        rs = st.executeQuery(sql);
        rs.first();
        return rs;
    } catch(Exception erro){
        Log.e("PostgreSQL","Erro: "+erro);
        return null;
    }
}

public void comandoPostgreSQL(String comando){
    try{
        st = conn.createStatement();
        st.execute(comando);
    } catch(Exception erro){
        Log.e("PostgreSQL","Erro: "+erro);
    }
}