Java中的toString方法打印符号表

Question

I'm doing a project where I build a simple symbol table consisting of two arrays : ArrayOfKeys and ArrayOfValues. The keys are words and the values are the frequencies of each word in a text. I need to write a toString method for my ST class using this model:

 public String toString() {
    // write your toString() method here
}

Suppose the words "aaa" and "bbb" are read from the text and inserted in the ST. The toString method will be called like this:

StdOut.println("Let's see ST1 with 4 pairs key-val: " + st1);

where "st1" is an instance of the ST class. The output should be this:

Let's see ST1 with 4 pairs key-val: {'aaa': 1 , 'bbb': 1}

As I see, the entire symbol table should be printed in the return statement of the toString() method, because it needs to return a String. I don't know how to do this, let alone in the format shown above.

The best I could try was:

return (arrayOfKeys + ":" + arrayOfValues);

PS: I'm using Java version 1.8.0_121.

Answer 1

One relatively neat (IMHO) approach is to create a stream of the indexes the arrays have and let Collectors.joining do the heavy lifting for you:

String result = 
    IntStream.range(0, arrayOfKeys.length)
             .mapToObj(i -> "'" + arrayOfKeys[i] + "': " + arrayOfValues[i])
             .collect(Collectors.joining(" , ", "{", "}"));

Answer 2

You can try using StringBuilder to generate the string. Code should look something like below:

public String toString() {
    StringBuilder sb = new StringBuilder("Let's see ST1 with 4 pairs key-val: {");
    for(int i = 0; i< arrayOfKeys.size();i++) {
        sb.append('\'' + arrayOfKeys[i] + '\': ');
        sb.append(String.valueOf(arrayOfValues[i]));
        if(i!=arrayOfKeys.size() -1) {
            sb.append(" , ");
        }
    }
    sb.append("}");
    return sb.toString();
}

Answer 3

 public String toString() {
    String results = "{";
    for (int i = 0; i < arrayOfKeys.length; i++){
        results += "'"+arrayOfKeys[i]+"' : "+arrayOfValue[i]+",";
    }
    results+="}";

    return results;
}