java编写一个代表三角形的类，其中3条边为三角形的属性，并封装有求三角形的面积和周长的方法。分别利用3条边为3、4、5和7、8、9的两个三角形进行测试。

好的，以下是Java代码实现：

public class Triangle {
    private double sideA;
    private double sideB;
    private double sideC;

    public Triangle(double sideA, double sideB, double sideC) {
        this.sideA = sideA;
        this.sideB = sideB;
        this.sideC = sideC;
    }

    public double getSideA() {
        return sideA;
    }

    public void setSideA(double sideA) {
        this.sideA = sideA;
    }

    public double getSideB() {
        return sideB;
    }

    public void setSideB(double sideB) {
        this.sideB = sideB;
    }

    public double getSideC() {
        return sideC;
    }

    public void setSideC(double sideC) {
        this.sideC = sideC;
    }

    public double getArea() {
        double p = (sideA + sideB + sideC) / 2;
        return Math.sqrt(p * (p - sideA) * (p - sideB) * (p - sideC));
    }

    public double getPerimeter() {
        return sideA + sideB + sideC;
    }
}

接下来进行测试：

public class Main {
    public static void main(String[] args) {
        Triangle t1 = new Triangle(3, 4, 5);
        System.out.println("t1: ");
        System.out.println("Area: " + t1.getArea());
        System.out.println("Perimeter: " + t1.getPerimeter());

        Triangle t2 = new Triangle(7, 8, 9);
        System.out.println("t2: ");
        System.out.println("Area: " + t2.getArea());
        System.out.println("Perimeter: " + t2.getPerimeter());
    }
}

输出结果为：

t1: 
Area: 6.0
Perimeter: 12.0
t2: 
Area: 26.832815729997478
Perimeter: 24.0

可以看到，输出结果符合预期，算法正确。