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Published byIrene Eaton Modified over 9 years ago
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7.1 Arrays
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7.1.1 Introduction to arrays Any array is a collection of objects or primitives Useful when the number of reference variables is large or can’t be determined until Runtime
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7.1.2 Variables in arrays An array is a collection of variables The variables are either a primitive or a reference to an object There is also a reference to the array itself
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7.1.3 Index Arrays are a built-in object All members of the array are of the same type and size Accessing array members is quick and efficient
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7.1.4 Arrays of primitives This example shows two arrays of primitives
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7.1.5 Arrays of objects Arrays of objects are a collection of references The array variable references the array object Each member of the array is itself a reference to another object
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7.2.1 Creating arrays Step 1: Declare the array reference variable int[] arrayOfInts; int arrayOfInts[]; Step 2: Create the array using the ‘new’ operator arrayOfInts = new int[5]; The array is then initialized to default values
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7.2.2 Use subscripts to access elements of an array Access the members of the array using an index Index is an int The index for the first member is 0 The following code creates an array of ints, then assigns a value to the 3 rd element Int[] myArray; myArray = new int[5]; myArray[2] = 57;
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7.3.1 Array of primitives Arrays of primitives can be assigned initial values when they are declared The array members can still be changed if necessary
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7.3.2 Array of objects Initializing arrays of objects requires that the objects be instantiated first, ie: Account[] accountList; accountList = new Account[2]; accountList[0] = new Account(203.50); accountList[1] = new Account(4500.00);
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7.4.1 Accessing array elements The index value must resolve to an int Can be an explicit value of the result of a calculation loopValue = arrayOfInts[index – 1]; System.arraycopy() can be used to copy the contents of one array to another System.arraycopy(arrayOfInts, 0, anotherArrayOfInts, 0, arrayOfInts.length);
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7.4.2 Using arrays An array can be a way of passing a large number of arguments to a method Parallel arrays can be used to store related information String names = new String[20]; String addresses = new String[20]; String phone = new String[20]; Char grades = new char[20]; Array members can be searched and sorted
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7.5.1 Multidimensional arrays Multidimensional arrays can be used instead of parallel arrays Declared with multiple sets of ‘[]’ int[][] multiArray = new int[20][30]; Use a separate index for each ‘dimension’ loopValue = multiArray[5][20];
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7.5.2 Traversing a multidimensional array Nested ‘for’ loops can be used to index all the elements of an array public int[][] myArray = new int[4][5]; for(x = 0; x < 4; x++) { for(y = 0; y < 5; y++) { myArray[x][y] = x * y; }
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