integer列表打印列表

Question

I have the following list:

List<List<int[]>> graph;

How can I print the content of graph without using loop? I tried the following 2 methods but all of them failed to print:

int[][] input=new int[][]{{1,2,5},{1,3,6},{2,3,1}};
List<List<int[]>> graph = new ArrayList<>();
        for (int i = 0; i <= 3; i++) graph.add(new ArrayList<>());
        for (int[] conn : input) {
            int city_A = conn[0], city_B = conn[1], price = conn[2];
            graph.get(city_A).add(new int[] {city_B, price});
            graph.get(city_B).add(new int[] {city_A, price});
        }
graph.forEach(s->System.out.println("Output:"+s));
System.out.println(Arrays.deepToString(graph.toArray()));

Output:[[I@1fb3ebeb, [I@548c4f57] Output:[[I@1218025c, [I@816f27d] Output:[[I@87aac27, [I@3e3abc88]

Expected output is to print each element without going to new line:

Output: [[1,2], [1,3], [2,0]]

Answer 1

Edit: the original question has changed.

I think what you actually want is a string representation of your graph.Have you tried a simple

System.out.println(graph);

?

Leaving the answer to the original question up, which was how to print all the integers in the inner list without using a traditional for loop.

graph.forEach(innerList -> {
    innerList.forEach(s-> System.out.println("Output: "+ s))
});

But why though..

Also the forEach is just the java functional library shorthand for a traditional for loop, so I'm not quite sure what you're gaining here. Hope that helps

Answer 2

Try this.

• graph.stream creates a stream of List<int[]>
• flatmap(List::stream) takes those lists and creates a single stream of int[]
• Arrays.toString takes an array and prints it separated by commas.

Note that printing an array is printing an object . Its default toString is what you see when you print it so it won't work. Arrays.toString() actually iterates over each element and returns a string that is printable.

    List<List<int[]>> graph = some list;

    graph.stream().flatMap(List::stream)
                .forEach(arr->System.out.print(Arrays.toString(arr) + " "));

More on printing arrays

Notice the numeric part (in hex) for printing out this array. The numeric part comes from the hashCode. Also the [I in front of the first output means a simple int array. [[I signifies an array of int arrays.

int[] arr1 = {1,2};
System.out.println(arr1); // prints [I@4617c264 on my machine
System.out.println(Integer.toHexString(arr1.hashCode()));

int[][] arr2 = {{1,2},{3,4}};
System.out.println(arr2); // prints [[I@36baf30c on my machine