编译时错误：找不到符号Jlabel

我在程序中找不到错误。我是新手，对您的帮助将不胜感激。我遇到了我不知道该如何解决的错误。我的完整代码如下：

 import java.awt.*;
 import javax.swing.*;
 import java.awt.event.*;

public class SampleApp3 extends JFrame{

Container pane;
JLabel label1;
JLabel label2;
Jlabel label3;
Jlabel label4;

 public SampleApp3(){
    pane=getContentPane();
    setSize(650, 540);
    setTitle("FormExample");
    pane.setLayout(null);

    label1= new JLabel("STI College Las Pinas",SwingConstants.CENTER);
    label1.setBackground(Color.yellow);
    label1.setToolTipText("Pogi Ako");
    label1.setForeground(Color.blue);
    pane.setBackground(Color.yellow);
    label1.setBounds(100,210,325,50);
    pane.add(label1,"Center");

    label2= new JLabel("Charles Jason Decena",SwingConstants.CENTER);
    label2.setBackground(Color.yellow);
    label2.setToolTipText("Si Charles ay Pogi");
    label2.setForeground(Color.blue);
    pane.setBackground(Color.yellow);
    label2.setBounds(110,215,320,48);
    pane.add(label2,"Center");

    label3= new JLabel("BSIT-124",SwingConstants.CENTER);
    label3.setBackground(Color.yellow);
    label3.setToolTipText("Ehem si Decena ay pogi");
    label3.setForeground(Color.blue);
    pane.setBackground(Color.yellow);
    label3.setBounds(120,220,315,46);
    pane.add(label3,"Center");

    label4= new JLabel("Computer Programming 2",SwingConstants.CENTER);
    label4.setBackground(Color.yellow);
    label4.setToolTipText("Well Pogi talaga ako");
    label4.setForeground(Color.blue);
    pane.setBackground(Color.yellow);
    label4.setBounds(130,225,315,44);
    pane.add(label4,"Center");

    }
public static void main(String args[]) {
    SampleApp3= new SampleApp3(); //and this one 
app.setVisible(true);
}
}

该错误消息说Jlabel3和4“不能找到符号”，并且还包含文本sampleapp3。谁能帮助我解决导致错误的原因？