提取超类

// File Class.java
public class Class {
    public int varInt;
    private double varDouble;
    public static final int CONSTANT = 0;
    public void publicMethod() {
        ...
    }
    public void hiddenMethod() {
        ...
    }
    public void setVarDouble(double var) {
        this.varDouble = var;
    }
    public double getVarDouble() {
        return
                  varDouble;
    }
}

// File Class.java
public class Class extends SuperClass {
    public int varInt;
    public void publicMethod() {
    ...
    }
    public void hiddenMethod() {
    ...
    }
}

// NEW file SuperClass.java
public abstract class SuperClass {
    private double varDouble;
    public static final int CONSTANT = 0;
    public abstract void publicMethod();
    public void setVarDouble(double var) {
        this.varDouble = var;
    }
    public double getVarDouble() {
        return varDouble;
    }
}