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41 import java.util.*;
42 import java.io.*;
43 import jas.*;
44
45 public class exprcomp implements RuntimeConstants
46 {
47 StreamTokenizer inp;
48 CodeAttr myCode;
49 short cur_stack_height;
50 short max_stack_height;
51 short max_vars;
52 Hashtable vars;
53
54 public exprcomp(StreamTokenizer inp)
55 throws jasError
56 {
57 inp.eolIsSignificant(false);
58 this.inp = inp;
59 myCode = new CodeAttr();
60 myCode.addInsn(new Insn(opc_aload_0));
62 myCode.addInsn(new Insn(opc_invokenonvirtual,
63 new MethodCP("java/lang/Object",
64 "<init>", "()V")));
65 cur_stack_height = max_stack_height = 1;
66 vars = new Hashtable();
67 max_vars = 1;
68 }
69 public void write(DataOutputStream out)
70 throws IOException, jasError
71 {
72 ClassEnv clazz = new ClassEnv();
73 myCode.setStackSize(max_stack_height);
74 myCode.setVarSize(max_vars);
75 clazz.addMethod
77 ((short) ACC_PUBLIC, "<init>", "()V", myCode, null);
78 clazz.setClassAccess((short) ACC_PUBLIC);
79 clazz.setClass(new ClassCP("results"));
80 clazz.setSuperClass(new ClassCP("java/lang/Object"));
81 clazz.write(out);
82 }
83
84 public void parse()
85 throws IOException, parseError, jasError
86 {
87 inp.nextToken();
88 while(inp.ttype != inp.TT_EOF)
89 {
90 if (inp.ttype != inp.TT_WORD)
91 {
92 throw new parseError("Expected an id at line " + inp.lineno());
93 }
94 if (inp.sval.equals("println"))
95 {
96 match(inp.TT_WORD);
97 expr();
98 match(';');
99 emit(new Insn(opc_getstatic,
100 new FieldCP("java/lang/System",
101 "out", "Ljava/io/PrintStream;")));
102 emit(new Insn(opc_swap));
103 emit(new Insn(opc_invokevirtual,
104 new MethodCP("java/io/PrintStream",
105 "println", "(I)V")));
106 }
107 else
108 { Integer  idx;
110 if ((idx = (Integer ) vars.get(inp.sval)) == null)
111 {
112 idx = new Integer (max_vars++);
113 vars.put(inp.sval.intern(), idx);
114 }
115 match(inp.TT_WORD); match('='); expr(); match(';');
116 emit(new Insn(opc_istore, idx.intValue()));
117 }
118 }
119 emit(new Insn(opc_return));
120 }
121
122 void expr()
123 throws IOException, parseError, jasError
124 {
125 term();
126 while (true)
127 {
128 switch(inp.ttype)
129 {
130 case '+':
131 match('+'); term(); emit(new Insn(opc_iadd)); break;
132 case '-':
133 match('-'); term(); emit(new Insn(opc_isub)); break;
134 default: return;
135 }
136 cur_stack_height--;
137 }
138 }
139
140 void term()
141 throws IOException, parseError, jasError
142 {
143 factor();
144 while (true)
145 {
146 switch(inp.ttype)
147 {
148 case '*': match('*'); factor(); emit(new Insn(opc_imul)); break;
149 case '/': match('/'); factor(); emit(new Insn(opc_idiv)); break;
150 default: return;
151 }
152 cur_stack_height --;
153 }
154 }
155 void factor()
156 throws IOException, parseError, jasError
157 {
158 switch(inp.ttype)
159 {
160 case '(': match('('); expr(); match(')'); break;
161 case inp.TT_NUMBER:
162 int val = (int)(inp.nval);
163 emit(new Insn(opc_bipush, (short)val));
164 match(inp.TT_NUMBER);
165 break;
166 case inp.TT_WORD:
167 Integer idx;
168 if ((idx = (Integer ) vars.get(inp.sval)) == null)
169 {
170 throw new parseError
171 ("Unknown variable " + inp.sval + " at line " + inp.lineno());
172 }
173 emit(new Insn(opc_iload, idx.intValue()));
174 match(inp.TT_WORD);
175 break;
176 default:
177 throw new parseError("Syntax error at line " + inp.lineno());
178 }
179 cur_stack_height++;
180 if (max_stack_height < cur_stack_height)
181 max_stack_height = cur_stack_height;
182 }
183 void match(int val)
184 throws IOException, parseError
185 {
186 if (inp.ttype != val)
187 { throw new parseError
188 ("line " + inp.lineno() + ": expected " + val + " but got " + inp); }
189 inp.nextToken();
190 }
191
192 void emit(Insn insn)
193 {
194 myCode.addInsn(insn);
195 }
196
197 public static void main(String argv[])
198 throws Exception
199 {
200 exprcomp compiler =
201 new exprcomp(new StreamTokenizer(new FileInputStream(argv[0])));
202 compiler.parse();
203 ByteArrayOutputStream data = new ByteArrayOutputStream();
204 compiler.write(new DataOutputStream(data));
205 dynaloader dl = new dynaloader(data.toByteArray());
206 dl.exec();
207 }
208 }
209
210 class dynaloader extends ClassLoader
211 {
212 Hashtable cache;
213 Class ex;
214
215 dynaloader(byte[] data)
216 throws ClassFormatError
217 {
218 cache = new Hashtable();
219 ex = defineClass(data, 0, data.length);
220 cache.put("results", ex);
221 resolveClass(ex);
222 }
223
224 void exec() throws Exception { ex.newInstance(); }
225 public synchronized Class loadClass(String name, boolean resolve)
226 throws ClassNotFoundException
227 {
228 Class c = (Class ) cache.get(name);
229 if (c == null)
230 {
231 c = findSystemClass(name);
232 cache.put(name, c);
233 }
234 if (resolve) resolveClass(c);
235 return c;
236 }
237 }
238
239
240 class parseError extends Exception
241 { parseError(String s) { super(s); } }
242
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Java API By Example, From Geeks To Geeks.