1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
|
<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN">
<html>
<head>
<meta name="generator" content=
"HTML Tidy for Linux/x86 (vers 1st February 2002), see www.w3.org">
<title>Variables</title>
</head>
<body bgcolor="#ffffff">
<h2>Variables</h2>
<h3>Locals Panel</h3>
<p>The values of variables are displayed in the local variables
panel. The values in that panel are updated as you single-step
through your program. The panel is displayed using a tree, so
objects show their field variable values as child nodes. You can
expand the nodes to examine the complex fields.</p>
<p>Objects are shown using the tilted box icon. The type of the
object is shown in parentheses. The number following the type
indicates the unique identifier used to identify this object in the
debuggee VM. This is not the hash code of the object, and the value
will change from one instance of the VM to another.</p>
<p>Nodes in the tree that are shown with a circular arrow indicate
that the variable is an object reference that refers back to an
object already shown higher up the variable tree hierarchy. It
indicates a loop in the object references, which would generally be
confusing if not clearly indicated.</p>
<p>Arrays are indicated with an icon that looks like a bulleted
list of three lines. The type of the array is shown in parentheses
and the size of the array is shown in brackets. Entries in the
array are shown as child nodes of the array. The number in brackets
is the array index and the type is shown in parentheses. The value
for the entry is shown following the colon. Double-clicking on the
"..." array entry will expand the entire array, showing
all of the array elements. This is not advisable for large
arrays.</p>
<h3>Watch Panel</h3>
<p>Another way of watching the values of field variables as they
change is with the watch panel. This panel allows you to watch any
field variable of any object as well as local variables. To watch a
variable, first suspend the debuggee VM using a breakpoint. Set the
breakpoint in a method that is within the scope of the variable to
be watched. When the debuggee VM stops, type the name of the
variable into the watch panel's empty "name" cell,
then press Enter. The watch panel will then display the changing
value of the variable as you single step through code.</p>
<p>The <code>this</code> keyword can be used to distinguish field
variables from like-named local variables. Objects are shown as the
string returned from their <code>toString()</code> method, if
possible. Otherwise they are shown as the string representation of
the JDI object.</p>
<p>To stop watching a variable, simply erase the name and press
Enter. The table row will be removed and the watch point will be
deleted. A popup menu for the panel allows you to remove all of the
watchpoints at once.</p>
<h3>Other Views of Variables</h3>
<p>Local variables can be displayed with the <code>locals</code>
command, which will display all the visible variables and their
values. However, this will not show field values of objects.
Instead, use the <code>dump</code> command described below.</p>
<p>To view the value of a single variable, use the
<code>print</code> command. This takes the name of a variable and
prints its value to the message window. The <code>print</code>
command can even take the name of an object with a reference to a
field variable. For example, if a local variable called
"date" is a Date object and you want to print the
"hourField" field variable of that object, you would type
'<code>print date.hourField</code>' at the command
prompt.</p>
<p>The <code>dump</code> command operates much like
<code>print</code> except that it shows all the field variables and
their values for the named object.</p>
<h3>Setting Variables</h3>
<p>Variable values can be modified using the <code>set</code>
command. See the command help for the syntax. The type of the value
on the right of the equals sign is ascertained by the type of the
variable referenced on the left side of the equals sign. That is,
if the variable being set is an Integer or int type, then the value
is interpreted as an integer.</p>
<p>Note that it is currently possible to set values that are meant
to be constants.</p>
</body>
</html>
|
