What's the simplest way to print a Java array?
In Java, arrays don't override toString() , so if you try to print one directly, you get the className + @ + the hex of the hashCode of the array, as defined by Object.toString() :
int[] intArray = new int[] {1, 2, 3, 4, 5};
System.out.println(intArray); // prints something like '[I@3343c8b3'
But usually we'd actually want something more like [1, 2, 3, 4, 5] . What's the simplest way of doing that? Here are some example inputs and outputs:
// array of primitives:
int[] intArray = new int[] {1, 2, 3, 4, 5};
//output: [1, 2, 3, 4, 5]
// array of object references:
String[] strArray = new String[] {"John", "Mary", "Bob"};
//output: [John, Mary, Bob]
Since Java 5 you can use Arrays.toString(arr) or Arrays.deepToString(arr) for arrays within arrays. Note that the Object[] version calls .toString() on each object in the array. The output is even decorated in the exact way you're asking.
Examples:
Simple Array:
String[] array = new String[] {"John", "Mary", "Bob"};
System.out.println(Arrays.toString(array));
Output:
[John, Mary, Bob]
Nested Array:
String[][] deepArray = new String[][] {{"John", "Mary"}, {"Alice", "Bob"}};
System.out.println(Arrays.toString(deepArray));
//output: [[Ljava.lang.String;@106d69c, [Ljava.lang.String;@52e922]
System.out.println(Arrays.deepToString(deepArray));
Output:
[[John, Mary], [Alice, Bob]]
double Array:
double[] doubleArray = { 7.0, 9.0, 5.0, 1.0, 3.0 };
System.out.println(Arrays.toString(doubleArray));
Output:
[7.0, 9.0, 5.0, 1.0, 3.0 ]
int Array:
int[] intArray = { 7, 9, 5, 1, 3 };
System.out.println(Arrays.toString(intArray));
Output:
[7, 9, 5, 1, 3 ]
Always check the standard libraries first. Try:
System.out.println(Arrays.toString(array));
or if your array contains other arrays as elements:
System.out.println(Arrays.deepToString(array));
This is nice to know, however, as for "always check the standard libraries first" I'd never have stumbled upon the trick of Arrays.toString( myarray )
--since I was concentrating on the type of myarray to see how to do this. I didn't want to have to iterate through the thing: I wanted an easy call to make it come out similar to what I see in the Eclipse debugger and myarray.toString() just wasn't doing it.
import java.util.Arrays;
.
.
.
System.out.println( Arrays.toString( myarray ) );
上一篇: 为什么Calendar.SEPTEMBER不工作？
下一篇: 打印Java数组最简单的方法是什么？