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Java > Open Source Codes > org > apache > bsf > debug > clientImpl > CircularBuffer


1 /*
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53  * please see <http://www.apache.org/>.
54  */
55
56 package org.apache.bsf.debug.clientImpl;
57
58
59 public class CircularBuffer {
60
61     Object JavaDoc m_elements[];
62     int m_pos,m_end;
63
64     public CircularBuffer() {
65         m_elements = new Object JavaDoc[256];
66     }
67     
68     /**
69      * Grow but be carefull that we might be already wrapped
70      * around where the end is before the current position
71      * (m_end<m_pos)
72      *
73      * |....E.... P....|
74      *
75      * in which case we have to grow the array and then
76      * copy the two parts:
77      * - 0 to E==m_end
78      * - P==m_pos to the end
79      * the free space is created in the middle (tmp.length
80      * free slots) and therefore m_pos needs to be updated.
81      */
82     private void grow() {
83         int p,q;
84         Object JavaDoc tmp[] = m_elements;
85         m_elements = new Object JavaDoc[2*m_elements.length];
86         if (m_pos<=m_end) {
87             for (p=m_pos;p<m_end;p++)
88                 m_elements[p] = tmp[p];
89         } else {
90             for (p=0;p<m_end;p++)
91                 m_elements[p] = tmp[p];
92
93             for (p=m_pos;p<tmp.length;p++)
94                 m_elements[p+tmp.length] = tmp[p];
95             
96             m_pos += tmp.length;
97         }
98     }
99
100     public synchronized void push(Object JavaDoc elem) {
101         
102       if (m_end==m_elements.length) {
103         // we are full but not warped,
104 // can we warp around?
105 if (m_pos==0) {
106             // no... therefore just grow.
107 grow();
108         } else {
109             // yes, warp;
110 m_end = 0;
111         }
112         m_elements[m_end++] = elem;
113         return;
114       }
115       if (m_pos<=m_end) {
116         // we are not wrapped and we
117 // are not full (above test)...
118 // just add the event.
119 m_elements[m_end++] = elem;
120         return;
121       }
122       // we are wrapped...
123 if (m_end==m_pos-1) {
124         // we are warpped and full, grow.
125 grow();
126       }
127       m_elements[m_end++] = elem;
128     }
129     //////////////////////////////////
130 public boolean isEmpty() {
131       return (m_pos==m_end);
132     }
133     //////////////////////////////////
134 public Object JavaDoc pop() {
135       Object JavaDoc elem;
136       
137       if (m_pos==m_end) return null;
138       elem = m_elements[m_pos++];
139       if (m_pos==m_elements.length &&
140           m_pos!=m_end)
141           m_pos=0;
142       return elem;
143     }
144     
145 }
146
147
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