CBSE Class 12 Informatics Practices Commonly Used Libraries Worksheet

CHAPTER 6: COMMONLY USED LIBRARIES

Libraries: It is a set of ready-made software routines that can be reused in new programs. Libraries are made available in a program using import statement e.g. import java.io.*; String Library: It is a part of java language library java.lang, which is by default imported to the program. There are 3 classes to work with characters:

(i) Character Class whose instances can hold single character data.

(ii) String Class whose instances can hold unchanging string. Every time we change, a new object is created automatically.

String s = “Excellent” ; or String s = new String(“Excellent”);

(iii) StringBuffer Class whose instances can hold mutable strings.

StringBuffer sb = new StringBuffer(); or StringBuffer sb = new StringBuffer(“First”); or

StringBuffer sb = new StringBuffer(10); // to hold 10 characters

String s = "crack", r = "rack";

Additional stringBuffer Methods:

Math Functions: It is found in Math library and used as Math.sqrt(a*a + b*c)

round(x): Rounds off a number to its nearest integer. It argument is double then it returns long and for float it returns int. If the argument is NaN, then the result is zero. Round(-4.5) is -4. Round(4.5) is 5. (NaN means Not a Number).

Sample Questions:

1. What will be display in a jTextField1 after executing the following code?
int m= 16; m=m+1;
if (m<15) jTextField. setText(Integer.toString(m)); else
jTextField1.setText(Integer.toString(m+15));

2. What does round() return if a negative float value is passed to it?

3. Write code to display IP 12 CBSE in a dialog box (JOptionPane).

4. What will be the output of the following code: (i) Math.round(1.5) (ii) “Welcome”.toUpperCase().

5. What will be the value X1 after the execution of the following code ?
String X1= "Graduate" ,X2="Post" ; X1=X2. concat (X1) ;