Java Certification SCJP : String

Here is common question about String.


Exercise :

public class test {

public static void main(String args) {
String s = "toto";
System.out.println("Size of s:" + s.length);
}
}


What is the result ? (choose one)

A Size of s:4
B Size of s:3
C Compilation fails
D An exception is thrown at runtime














Solution :

The answer is C because String have a method that's call length() but it has no attribute length.
Note that it's really easy to be a mistake here !

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Exercice certification SCJP

Here is a small SCJP exercice to practice :


Given the following :

public class Test {

public int myTest = 2;
private String str;
public static void main(String [] args) {

for(int i=1;i<12;i++){
int myValue = 2;
System.out.println("great test !");
if (i== 5) {
myValue++;
System.out.println("myValue=" + myValue);
}
}
myValue++;
System.out.println("myValue=" + myValue);
}
}

What is the result ? (choose one)

A myValue=3 myValue=4
B myValue=3 myValue=3
C Compilation fails
D An exception is thrown at runtime








Solution

The solution is C because myValue exist only in for statement.

SCJP exercise : private, protected and public

Exercise :

public class Test {

public int myTest = 2;
private String str;
public static void main(String [] args) {
System.out.println("myTest=" + myTest);

}

}

What is the result ? (choose Two)

A myTest=2
B myTest=0
C Compilation fails
D An exception is thrown at runtime







Solution

C . The compilation will fail because we are in the main() method and we haven't instantiate Test.To make it working on solution should be :
Test monTest = new Test();
System.out.println("monTest=" + monTest.myTest);

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SCJP exercise : identifiers

Exercise 1 :

Given the following :

public class Test {
public static void main(String [] args) {
int $test = 10;
System.out.println("$test=" + $test);

}

}

What is the result ? (choose Two)

A $test=10
B $test=null
C Compilation fails
D An exception is thrown at runtime


Exercise 2

Given the following :

public class Test {
public static void main(String [] args) {
int $2test = 10;
System.out.println("$2test=" + $2test);

}

}

What is the result ? (choose Two)

A $2test=10
B $test=null
C Compilation fails
D An exception is thrown at runtime














Solution Exercise 1 :

The solution is A. An identifier can begin with $ or _ .

Solution Exercice 2 :

The correct answer is A. An identifier can't begin with a number but can have a number.

SCJP exercices

Hi all,

I will publish some SCJP exercices next saturday and every week.
All comments will be appreciate !