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Programmer Certification (OCPJP)
Arrays sort doubt.
Ramamoorthy Periasamy
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Posts: 30
posted 17 years ago
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package scjp.exam; import java.util.*; class pen implements Comparable<pen> { int size; pen(int s) { size = s; } public int compareTo(pen p) { return this.size - p.size; } public String toString() { return "" + size; } } class penc implements Comparator<pen> { public int compare(pen p1, pen p2) { return p2.size - p1.size; } } public class CollectionTest1 { public static void main(String[] args) { pen[] pa = new pen[3]; pa[0] = new pen(4); pa[1] = new pen(2); penc pc = new penc(); Arrays.sort(pa, pc); // NullPointerException } }
Can you please help me out how to do Arrays.sort()? I am getting runtime exception. Did I miss anything in the code. Please advice
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Gowher Naik
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posted 17 years ago
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package scjp.exam; import java.util.*; class pen implements Comparable<pen> { String size; pen(String s) { this.size = s; } public int compareTo(pen p) { return this.size.compareTo(p.size); } public String toString() { return "" + size; } } class penc implements Comparator<pen> { public int compare(pen p1, pen p2) { return p2.size.compareTo(p1.size); } } public class CollectionTest1 { public static void main(String[] args) { pen[] pa = new pen[2]; pa[0] = new pen("4"); pa[1] = new pen("2"); penc pc = new penc(); Arrays.sort(pa, pc); // NullPointerException for(pen o :-P a){ System.out.println(o); } } }
check code above which is modified version of your code and
try to find where you have made mistakes.
Hint-: Comparator cannot be used with primitive arrays.
Neelesh Bodas
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Posts: 107
posted 17 years ago
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This is because pa[2] is a null reference.
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is non-stick and lasts a lifetime.
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