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import junit.framework.TestCase;
public class TestMyStack extends TestCase {
public void testEmpty() throws Exception {
MyStack stack = new MyStack();
stack.checkInvariant();
stack.push("sample");
stack.checkInvariant();
assertEquals("sample", stack.pop());
stack.checkInvariant();
stack.delete(1);
stack.checkInvariant();
}
}
class MyStack {
public MyStack() {
stack = new String[100];
next_index = 0;
}
public String pop() {
return stack[--next_index];
}
public void delete(int n) {
next_index -= n;
}
public void push(String aString) {
stack[next_index++] = aString;
}
public String top() {
return stack[next_index - 1];
}
public void checkInvariant() throws Exception {
if (!(next_index >= 0 && next_index < stack.length)) {
throw new Exception("next_index out of range: " + next_index + " for stack length "
+ stack.length);
}
}
private int next_index;
private String[] stack;
}
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