// FractionSpring.java
// A Spring extension that calculates its values based on an anchor Spring
// and a multiplier (> 0.0).  Note that values greater than 1.0 can be
// used.
//

import javax.swing.Spring;

public class FractionSpring extends Spring {

  protected Spring parent;
  protected double fraction;

  public FractionSpring(Spring p, double f) {
    if (p == null) {
      throw new NullPointerException("Parent spring cannot be null");
    }
    parent = p;
    fraction = f;
  }

  public int getValue() {
    return (int)Math.round(parent.getValue() * fraction);
  }

  public int getPreferredValue() { 
    return (int)Math.round(parent.getPreferredValue() * fraction);
  }
  public int getMinimumValue() { 
    return (int)Math.round(parent.getMinimumValue() * fraction);
  }
  public int getMaximumValue() { 
    return (int)Math.round(parent.getMaximumValue() * fraction);
  }

  public void setValue(int val) {
    // Uncomment this next line to watch when our spring is resized:
    // System.err.println("Value to setValue: " + val);
    if (val == UNSET) {
      return;
    }
    throw new UnsupportedOperationException(
         "Cannot set value on a derived spring");
  }

  public static FractionSpring half(Spring s) {
    return new FractionSpring(s, 0.5);
  }
}