Math expression parser in java

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Java

Consider an expression like E:

123 * x + 456 * y * 12 - 200 / z

which follows the rules:
1. may contain operands: +,-,*,/
2. may contain variables (like 'x')
3. may contain constants (like '123')
4. does not contain parenthesis.

Focus should be put on good use of OOP principles.

Can someone help me to write a set of Java classes to accomplish this?

What I have tried:

I have tried using ScriptEngine. However I cant use those ScriptEngine.

ScriptEngine engine = new ScriptEngineManager().getEngineByName("JavaScript");
System.out.println("result = " + engine.eval(expr, new SimpleBindings(vars)));