<html>
<head>
<title>Java</title>
</head>
<body>
<form name="f1">
<input type="text" name="txt">
<input type="button" onclick="f1.txt.value += 1" value="1">
<input type="button" onclick="f1.txt.value += 2" value="2">
<input type="button" onclick="f1.txt.value += this.value" value="3">
</form>
</body>
</html>