1. String behaviour.
package com.thebeautifuljava.certificationprograms;
public class Test1 {
public static void main(String[] args) {
String str1 = "abc"; // object is created in string constant pool
String str2 = "def"; // object is created in string constant pool
String str3 = str1.concat(str2); // str3 = "abc".concat("def")
// str3 points to the new object "abcdef" in pool and heap
// (Refer String chaper in Java 6 Kathy Sierra and Bert Bates)
str1.concat(str2); // "abc".concat("def") => "abcdef" (No reference). This object is already present in pool and
// new object "abcdef" is created in heap also!
// (Refer String chaper in Java 6 Kathy Sierra and Bert Bates)
System.out.println(str1); // str1 still points to object "abc" as
// str1 reference is not updated!!
}
}
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2. ceil() and round() methods of Math class.
package com.thebeautifuljava.certificationprograms;
public class Test2 {
public static void main(String args[]) {
int i;
float f = 2.3f;
double d = 2.7;
i = ((int) Math.ceil(f)) * ((int) Math.round(d)); // i = ((int) 3.0) * ((int) 3) => i = // (3 * 3) => i = 9
System.out.println(i); // prints 9
}
}
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3. Post decrement operator behaviour.
package com.thebeautifuljava.certificationprograms;
public class Test3 {
public static void main(String args[]) {
int i = 1;
do {
i--; // i=1
} while (i > 2); // i=0, (0 > 2)? - false
System.out.println(i); // prints 0
}
}
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4. Difference between == operator and equals() method of Object class.
package com.thebeautifuljava.certificationprograms;
public class Test4 {
/**
* @param args
*/
public static void main(String[] args) {
// TODO Auto-generated method stub
String s1 = "abc"; // memory is allocated in string constant pool
String s2 = new String("abc"); // memory is allocated in heap and "abc" literal is created in pool also!
// (Refer String chaper in Java 6 Kathy Sierra and Bert Bates)
if (s1 == s2) // false - as s1 and s2 points to different memory locations
System.out.println(1);
else
System.out.println(2); // prints 2
if (s1.equals(s2)) // true - ("abc".equals("abc"))?
// as equals method compares String object's contents
System.out.println(3); // prints 3
else
System.out.println(4);
}
}
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5. Post increment and decrement operator.
package com.thebeautifuljava.certificationprograms;
public class Test6 {
/**
* @param args
*/
public static void main(String[] args) {
// TODO Auto-generated method stub
int i = 1, j = 1;
try {
i++; // i=1
j--; // j=1, i=2
if (i == j) // j=0 => (2==0)? - false
i++;
} catch (ArithmeticException e) {
System.out.println(0);
} catch (ArrayIndexOutOfBoundsException e) {
System.out.println(1);
} catch (Exception e) {
System.out.println(2);
} finally {
System.out.println(3); // prints 3 (because no exception)
}
System.out.println(4); // prints 4 (executes after finally block)
}
}
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6. Pre increment and post decrement operator.
package com.thebeautifuljava.certificationprograms;
public class Test7 {
/**
* @param args
*/
public static void main(String[] args) {
// TODO Auto-generated method stub
int i = 0, j = 2;
do {
i = ++i; // i=1 => i=2
j--; // j=1 => j=0
} while (j > 0); // (1 > 0)? - true => (0 > 0)? - false
System.out.println(i);
}
}
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7. switch-case statement.
package com.thebeautifuljava.certificationprograms;
public class Test8 {
/**
* @param args
*/
public static void main(String[] args) {
// TODO Auto-generated method stub
int i, j = 1;
i = (j > 1) ? 2 : 1; // (1 > 1)?2 : 1 - false and i=1
switch (i) { // switch(1)
case 0:
System.out.println(0);
break;
case 1:
System.out.println(1); // prints 1 (because no break statement after case 2)
case 2:
System.out.println(2); // prints 2
break;
case 3:
System.out.println(3);
break;
}
}
}
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8. Assignment operator, wrapper class and array.
command line - java Test9 5
package com.thebeautifuljava.certificationprograms;
public class Test9 {
/**
* @param args
*/
public static void main(String[] args) {
// TODO Auto-generated method stub
Integer intObj = Integer.valueOf(args[args.length - 1]); // args[1-1] => args[0]
int i = intObj.intValue(); // args[0] = 5 - command line argument
if (args.length > 1) // false - args.length = 1 (1 > 1)?
System.out.println(i);
if (args.length > 0) // true - args.length = 1 (1 > 0)?
System.out.println(i - 5); // executes i=i-5, updated i's value is 0
else
System.out.println(i - 2);
}
}
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9. for-loop working.
package com.thebeautifuljava.certificationprograms;
public class Test10 {
/**
* @param args
*/
public static void main(String[] args) {
// TODO Auto-generated method stub
for (int i = 0; i < 2; i++) { // First iteration i=0, Second iteration i=1
for (int j = 2; j >= 0; j--) { // 2 iterations j=2,1, 1 iteration
if (i == j) // Second iteration of inner loop - i=1,j=1 condition is true
break;
System.out.println("i=" + i + " j=" + j); // prints i=0,j=1 i=0,j=2 i=1,j=2 for 3 iterations
}
}
}
}
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