Java String数组：如何检查数组是否有值？

Question

I'm making a program in java that will use a string array say:

String[] category = new String[46];

Then I will check if the array in a for loop if it already has a value,

for(int checking = 21; checking <= 45 ;checking++) {
    if(category[checking]=INSERT_HERE) {
        textArea += category[checking] + "\n";
    }
}

What do I put in INSERT_HERE? Note: textArea is a named JTextArea .

Answer 1

If you are making a check if the value is not null, then use

if(category[checking]!=null)

And if you are making a check for some particular value, then

if(category[checking].equals(PARTICULAR_VALUE))

PS: '=' is for assignment, you should use '==' for comparison.

Answer 2

for(int checking=21;checking<=45;checking++) {
    if(category[checking] != null || category[checking] != "") {
       textArea += category[checking] +"\n";
    }
}

Answer 3

您必须检出它是否不为null，如下所示：

 if(category[checking] != null) // will check all filled values only

Answer 4

When you define your array as

String[] category=new String[46];

you allocate 46 reference slots in memory for your array. These slots are initially null , so when you need to do a comparison like the one you asked, you need to check against null .

...
if(category[checking] != null)
...

Answer 5

You could try something like that in your code:

for(int checking=21;checking<=45;checking++) {
    if(category[checking] != null) {
        textArea+=category[checking] +"\n";
    }
}

Or like that:

for(int checking=21;checking<=45;checking++) {
    if(category[checking] != "") {
        textArea+=category[checking] +"\n";
    }
}