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  1. /* package whatever; // don't place package name! */
  2.  
  3. import java.util.*;
  4. import java.lang.*;
  5. import java.io.*;
  6.  
  7. /* Name of the class has to be "Main" only if the class is public. */
  8. class Ideone
  9. {
  10. 	interface Expression {
  11. 		public double evaluate();
  12. 	}
  13.  
  14. 	static class UnaryExpression implements Expression {
  15. 		boolean positiveOperator;
  16. 		Expression operand;
  17.  
  18. 		public UnaryExpression(Expression operand, boolean positive) {
  19. 			this.operand = operand;
  20. 			this.positiveOperator = positive;
  21. 		}
  22.  
  23. 		@Override
  24. 		public double evaluate() { 
  25. 			double value = operand.evaluate();
  26. 			return positiveOperator ? value : -value;
  27. 		}
  28. 	}
  29.  
  30. 	static class ConstantExpression implements Expression {
  31. 		double value;
  32.  
  33. 		public ConstantExpression(double value) {
  34. 			this.value = value;
  35. 		}
  36.  
  37. 		@Override
  38. 		public double evaluate() { return this.value; }
  39. 	}
  40.  
  41. 	static class BinaryExpression implements Expression {
  42. 		Expression left;
  43. 		Expression right;
  44. 		int operator;
  45.  
  46. 		public static final int PLUS = 0;
  47. 		public static final int MINUS = 1;
  48. 		public static final int MULTIPLY = 2;
  49. 		public static final int DIVIDE = 3;
  50.  
  51. 		public BinaryExpression(Expression left, Expression right, int operator) {
  52. 			this.left = left;
  53. 			this.right = right;
  54. 			this.operator = operator;
  55. 		}
  56.  
  57. 		@Override
  58. 		public double evaluate() {
  59. 			double lValue = left.evaluate();
  60. 			double rValue = right.evaluate();
  61.  
  62. 			switch(operator) {
  63. 				case PLUS:
  64. 					return lValue + rValue;
  65. 				case MINUS:
  66. 					return lValue - rValue;
  67. 				case MULTIPLY:
  68. 					return lValue * rValue;
  69. 				case DIVIDE:
  70. 					return lValue / rValue;
  71. 				default:
  72. 					throw new IllegalStateException("Cannot execute operator: " + operator);
  73. 			}
  74. 		}
  75. 	}
  76.  
  77. 	public static void main (String[] args) throws java.lang.Exception
  78. 	{
  79. 		ConstantExpression two = new ConstantExpression(2);
  80. 		ConstantExpression three = new ConstantExpression(3);
  81. 		UnaryExpression negTwo = new UnaryExpression(two, false);
  82. 		BinaryExpression result = new BinaryExpression(negTwo, three, BinaryExpression.PLUS);
  83.  
  84. 		System.out.println(result.evaluate());
  85. 	}
  86. }
Success #stdin #stdout 0.09s 320576KB
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1.0
https://ideone.com/NWnuQG
language:
Java (HotSpot 12)
created:
8 years ago
visibility:
public

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