使用java语言，定义一个父类形状，其中包括求形状面积的方法。继承该类定义三角形，矩形，圆。分别创建一个三角形、矩形、圆，将各类图形的面积输出。

下面是Java代码实现：

public class Shape {
    public double area() {
        return 0.0;
    }
}

class Triangle extends Shape {
    private double base;
    private double height;

    public Triangle(double base, double height) {
        this.base = base;
        this.height = height;
    }

    @Override
    public double area() {
        return 0.5 * base * height;
    }
}

class Rectangle extends Shape {
    private double width;
    private double height;

    public Rectangle(double width, double height) {
        this.width = width;
        this.height = height;
    }

    @Override
    public double area() {
        return width * height;
    }
}

class Circle extends Shape {
    private double radius;

    public Circle(double radius) {
        this.radius = radius;
    }

    @Override
    public double area() {
        return Math.PI * radius * radius;
    }
}

public class Main {
    public static void main(String[] args) {
        Triangle triangle = new Triangle(3, 4);
        Rectangle rectangle = new Rectangle(5, 6);
        Circle circle = new Circle(7);

        System.out.println("Triangle area: " + triangle.area());
        System.out.println("Rectangle area: " + rectangle.area());
        System.out.println("Circle area: " + circle.area());
    }
}

输出结果为：

Triangle area: 6.0
Rectangle area: 30.0
Circle area: 153.93804002589985