Something wrong in my coding in java with numbers and strings

I tried to develop a java program using netbeans in which a GUI accepts subject marks from five text fields and displays the total marks, percentage and the grade in their respective text fields. The problem is I am getting errors while executing the GUI. I tried replacing int with double to hold decimal values of percentage but that didn't help. I am unable to find any errors and since I am a beginner i am unable to understand the errors given in the monitor by my netbeans. Please help.

ERRORS: Exception in thread "AWT-EventQueue-0" java.lang.NumberFormatException: For input string: " 34" at java.lang.NumberFormatException.forInputString(NumberFormatException.java:65) at java.lang.Integer.parseInt(Integer.java:481) at java.lang.Integer.parseInt(Integer.java:527) at NewJFrame.submit_buttonActionPerformed(NewJFrame.java:173) at NewJFrame.access$000(NewJFrame.java:4) at NewJFrame$1.actionPerformed(NewJFrame.java:60)

Here's the coding I've done.

        int sub1_ = Integer.parseInt(sub1.getText());
    int sub2_ = Integer.parseInt(sub2.getText());
    int sub3_ = Integer.parseInt(sub3.getText());
    int sub4_ = Integer.parseInt(sub4.getText());
    int sub5_ = Integer.parseInt(sub5.getText());

    // Here each subject holds a max. of 100 marks.

    int a = sub1_+sub2_+sub3_+sub4_+sub5_;
    total_marks.setText(""+a);

    // Since each subject holds a max. of 100 marks, the total marks of five subjects sums up to 500.

    int b = (a/500)*100;
    percentage.setText(b+"%");

    if(b<=100&&b>=91)
    {grade.setText("A1");}

    else if(b<=90&&b>=81)
    {grade.setText("A2");}

    else if(b<=80&&b>=71)
    {grade.setText("B1");}

    else if(b<=70&&b>=61)
    {grade.setText("B2");}

    else if(b<=60&&b>=51)
    {grade.setText("C1");}

    else if(b<=50&&b>=35)
    {grade.setText("C2");}

    else if(b<=34&&b>=0)
    {grade.setText("D");}

    else {grade.setText("");}