arrayHistogram implementation
you need to add some spaces in between operators and format the code properly

all I did here was


added spaces between operators
moved the curly braces to their appropriate locations for Egyptian Style Bracing
set indentation to standard, you had some lines that were indented and they shouldn't have been




public static void main(String[] args) {
    int[] array = randomIntArray(30); //declares the dimensions of the array "randomIntArray"
    System.out.println("Scores:");
    printArray(array); //calls the scoreHist method to print the "array variable
    System.out.println("\n" + "count: ");
    printArray(arrayHist(array)); //calls score hist, to call arrayHist, to count "array"
    System.out.println();
}
public static int randomInt(int low, int high) { //the prng
    double e;
    double x=Math.random();
    e=low+x*(high-low);
    return (int)e;
}
public static int[] randomIntArray(int n) { //generates an array of random numbers based on an upper and lower bound
    int[] a = new int[n];
    for(int i = 0; i &lt; a.length; i++) {
        a[i] = randomInt(-5, 15);
    } //"-5&amp;15 are the lower and upper bounds of the random number array
    return a;
}
public static int inRange(int[] a, int low, int high) { //checks if the numbers of the random number array are in certain constraints.
    int count = 0;
    for(int i = 0; i &lt; a.length; i++) {
        if(a[i] &gt;= low &amp;&amp; a[i] &lt;= high) count++;
    }
    return count;
}
public static int[] arrayHist(int[] scores) { //counts how many of each number occurs in "randomIntArray"
    int[] counts=new int[11];
    for(int i=0;i&lt;10;i++) {
        counts[i] = inRange(scores, i, i++);
    }
    return counts;
}
public static void printArray(int[] a) { //prints any array, with only one traversal.
    for(int i = 0; i &lt; a.length; i++) {
        System.out.print(" " + a[i]);
    }
}




I noticed that you are using a For loop, and I think that you should be using more foreach loops.  I am going to use this code as an example


public static int inRange(int[] a, int low, int high) { //checks if the numbers of the random number array are in certain constraints.
    int count = 0;
    for(int i = 0; i &lt; a.length; i++) {
        if(a[i] &gt;= low &amp;&amp; a[i] &lt;= high) count++;
    }
    return count;
}



so what you get is now this

public static int inRange(int[] a, int low, int high) {
    int count = 0;
    for(int i : a) {
        if(i &gt;= low &amp;&amp; i &lt;= high) count++;
    }
    return count;
}


which is slightly cleaner than the OP.

I also removed the comments on this method, mainly because they were unnecessary. you have a lot of comments in this code some of which are not needed at all, probably all of them.  most of your variables are named appropriately so you don't have a doubt what they stand for.  nothing is too complex here that you would need to explain what is going on. 

here are the comments I would get rid of


//declares the dimensions of the array "randomIntArray"
//declares the dimensions of the array "randomIntArray"
//the prng 


Here is the only comment that I would keep  

//counts how many of each number occurs in "randomIntArray"


on the ArrayHist Method. because the Method name doesn't really tell me that right away.



All Methods should be named in PascalCase, variables in camelCase.