Initial commit

Example_src/Chapter1-10/src/ch04/TestAddChengji.java

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+package ch04;
+
+import java.applet.*;
+import java.awt.*;
+
+class Chengji {
+    float fun(float x, float y) {
+        return x * y;
+    }
+}
+
+class AddChengji extends Chengji {
+    float fun(float x, float y) {
+        return x + y;
+    }
+}
+
+public class TestAddChengji extends Applet {
+    AddChengji sum;
+
+    public void init() {
+        sum = new AddChengji();
+    }
+
+    public void paint(Graphics g) {
+        g.drawString("sum=" + sum.fun(4, 6), 100, 40);
+    }
+}
+