Update java-basic-questions-01.md

printf 可以复现注释后的小数点数据

docs/java/basis/java-basic-questions-01.md

@@ -665,7 +665,7 @@ private static long sum() {
 ```java
 float a = 2.0f - 1.9f;
 float b = 1.8f - 1.7f;
-System.out.println(a);// 0.100000024
+System.out.printf("%.9f",a);// 0.100000024
 System.out.println(b);// 0.099999905
 System.out.println(a == b);// false
 ```