（1）合理定義一個三角形類Triangle，成員屬性包括3條邊，能否構成三角形的標誌；成員方法包括構造方法、修改3條邊、計算面積。

（2）寫一測試類，測試自定義三角形類Triangle是否正確。

class Triangle_D{
	private double f_edge;		//第一條邊
	private double s_edge;		//第二條邊
	private double t_edge;		//第三條邊
	
	public Triangle_D() {
		
	}
	
	//判斷能否構成三角形
	public Triangle_D(double  f_edge, double s_edge, double t_edge) {
		this.f_edge = f_edge;
		this.s_edge = s_edge;
		this.t_edge = t_edge;
		/*
		if(f_edge + s_edge > t_edge) {
			if(f_edge + t_edge > s_edge) {
				if(t_edge + s_edge > f_edge) {
					System.out.println("能構成三角形");
				}else {
					System.out.println("不能構成三角形，請重新輸入！");
				}
			}else {
				System.out.println("不能構成三角形，請重新輸入！");
			}
		}else {
			System.out.println("不能構成三角形，請重新輸入！");
		}
		*/
	}
	
	//獲取f_edge
	public void setF_edge(double f_edge) {
		this.f_edge = f_edge;
	}
	
	public double getF_edge(double f_edge) {
		return f_edge;
	}
	
	//獲取s_edge
	public void setS_edge(double s_edge) {
		this.s_edge = s_edge;
	}
	
	public double getS_edge(double s_edge) {
		return s_edge;
	}
	
	//獲取t_edge
	public void setT_edge(double t_edge) {
		this.t_edge = t_edge;
	}
	
	public double getT_edge(double t_edge) {
		return t_edge;
	}
	
	//構建judge判斷方法，判斷是否兩邊之和大於第三邊
	public boolean judge() {
		//語法正確，結果不符的寫法：
		//if((f_edge+s_edge>t_edge) || (f_edge+t_edge>s_edge) || (t_edge+s_edge>f_edge))
		if((f_edge+s_edge>t_edge) && (f_edge+t_edge>s_edge) && (t_edge+s_edge>f_edge)) {
			return true;
		}else {
			return false;
		}
	}
	
	public void area() {
		//立個flag
 		boolean flag = true;
		//定義變數半周長p，面積area
		double p, area;
		
		//判斷flag
		if (flag == judge()) {
			//計算半周長p
			p = (f_edge+s_edge+t_edge)/2;
			//計算面積，用到Math類sqrt方法
			area = Math.sqrt(p*(p-f_edge)*(p-s_edge)*(p-t_edge));
			System.out.println("輸入的數為"+f_edge+"\t"+s_edge+"\t"+t_edge);
			System.out.println("面積為："+area);
		}else {
			System.out.println("不能構成三角形，請重新賦值！");
		}
	}
}

//測試類
public class Triangle {

	public static void main(String[] args) {
		System.out.println("請輸入三個數字，來構成一個三角形");
		
		//建立物件
		Triangle_D td = new Triangle_D(3,4,5);
		td.area();
		//分割線
		System.out.println("-------------------分割線---------------------");
		//再次給值
		Triangle_D td2 = new Triangle_D(1,3,5);
		td2.area();
	}

}