arrays - Java error: non-static method cannot be referenced from a static context -

i know common error noobs myself, can't seem read can understand. homework need create array of longs called numberlist. 1 of methods need complete called tostring, turns array string print.

1. so in main method created blank numberlist object , tried running tostring() method on it. compiler says "non-static method tostring() cannot referenced static context". why!?
2. secondly, created test array of longs want pass numberlist object. called array testexample , made arbitrary values. when write

new numberlist(testexample);

i more errors. why can not this?

finally here's code. please ignore every method except main, constructors, , tostring.

thank much

public class numberlist implements java.util.collection {  //instance stuff private long[] longarray;  public static void main ( string[] args ) {      long[] testexample;     testexample = new long[3];          testexample[0] = 1;     testexample[1] = 2;     testexample[2] = 3;      new numberlist();     //system.out.println(     numberlist.tostring();     //);  }   /** constructs empty number list. */ public numberlist(){     longarray = new long[0];          //system.out.println(longarray.length); }   /** constructs number list array of longs. */ public numberlist( long[] l ){     int size = l.length;     longarray = new long[size];     (int = 0; < size; i++) {         longarray[i] = l[i];     } }   /** returns stringy version of number list. */ public string tostring () {     //system.out.println(this.length());     return "why doesnt work :("; }     /** increases 1 number of instances of given element in collection. */ public boolean add ( object obj ) {     /* replace next statement code */     //return true if element can added     throw new unsupportedoperationexception(); }   /** adds of elements of given number list one. */ public boolean addall ( java.util.collection c  ) {     /* replace next statement code */     throw new unsupportedoperationexception(); }   /** removes of elements collection. */ public void clear () {     /* replace next statement code */     throw new unsupportedoperationexception(); }   /** returns true iff number list contains @ least 1 instance of specified element. */ public boolean contains ( object obj ) {     /* replace next statement code */     //     throw new unsupportedoperationexception(); }    /** returns true iff number list contains @ least 1 instance of each element      in specified list. multiple copies of element in argument not     require multiple copies in number list. */ public boolean containsall ( java.util.collection c ) {     /* replace next statement code */     throw new unsupportedoperationexception(); }     /** compares specified object collection equality. */ public boolean equals ( object obj ) {     /* replace next statement code */     throw new unsupportedoperationexception(); }     /** returns hashcode value collection. */ public int hashcode () {     /* replace next statement code */     //return integer represents set uniquely     //return hashcode based on numbers in array     //hashcode should equal in equal cases     throw new unsupportedoperationexception(); }    /** returns true if collection contains no elements. */ public boolean isempty () {     /* replace next statement code */     throw new unsupportedoperationexception(); }    /** returns iterator on elements in collection. replicated elements should     "iterated over" once. */ public java.util.iterator iterator () {     /* replace next statement code */     throw new unsupportedoperationexception(); }    /** removes single instance of specified element      collection, if present. */ public boolean remove ( object obj ) {     /* replace next statement code */     throw new unsupportedoperationexception(); }    /** removes of collection's elements contained      in specified collection. */ public boolean removeall ( java.util.collection c ) {     /* replace next statement code */     throw new unsupportedoperationexception(); }     /** retains elements in collection contained in specified collection.       in other words, removes collection of elements not contained in       specified collection. */ public boolean retainall ( java.util.collection c ) {     throw new unsupportedoperationexception(); }   /** returns number of elements in number list, including duplicates. */ public int sizeincludingduplicates () {     /* replace next statement code */     throw new unsupportedoperationexception(); }    /** returns long[] containing of elements in collection, not including duplicates. */ public long[] toarray () {     /* replace next statement code */     throw new unsupportedoperationexception(); }    /** not supported class. */ public object[] toarray ( object[] obj ) {     throw new unsupportedoperationexception(); }     /** returns number of elements in number list, not including duplicates. */ public int size () {     system.out.println(longarray.length);     return 0 ; }     /** returns number of instances of given element in number list. */ public int count ( object obj ) {     /* replace next statement code */     throw new unsupportedoperationexception(); }    /** so-called "static factory" returns new number list comprised of numbers in specified array.     note given array long[], not long[]. */ public static numberlist fromarray ( long[] l ) {     /* replace next statement code */     throw new unsupportedoperationexception(); } 

}

it's not static method, tostring on numberlist can called on instance of object numberlist.

you must use

//create instance of nlist numberlist nlist = new numberlist(); //call method on newly created instance of numberlist nlist.tostring();