'NOT' 运算符 （！） 在与 Java 中的方法一起使用时如何工作？[关闭]

问：

以下是使用访问修饰符来避免生成异常的示例：

class FailSoftArray {
    private int a[];
    private int errval;
    public int length;

    public FailSoftArray(int size, int errv) {
        a = new int[size];
        errval = errv;
        length = size;
    }

    public int get(int index) {
        if(indexOK(index)) return a[index];
        return errval;
    }

    public boolean put(int index, int val) {
        if(indexOK(index)) {
            a[index] = val;
            return true;
        }
        return false;
    }
    private boolean indexOK(int index) {
        if(index >= 0 & index < length) return true;
        return false;
    }
}

public class TestMethod {
    public static void main(String[] args) {
        FailSoftArray333 fs = new FailSoftArray(5, -1);
        int x;

        System.out.println("\nError access message.");
        for(int i = 0; i < (fs.length * 2); i++)
            if(!fs.put(i, i*10))
                System.out.println("Index " + i + " outside the range of the array");

        for(int i =0; i < (fs.length * 2); i++) {
            x = fs.get(i);
            if(x != -1) System.out.print(x + " ");
            else
                System.out.println("Index " + i + " outside the range of the array");
        }
    }
}

我不明白为什么在这种情况下我必须使用运算符 （！） 才能使代码正常工作：

        System.out.println("\nError access message.");
        for(int i = 0; i < (fs.length * 2); i++)
            if(!fs.put(i, i*10))
                System.out.println("Index " + i + " outside the range of the array");

当我用 （！） 打印它时，结果是你所期望的：

Error access message..
Index 5 outside the range of the array
Index 6 outside the range of the array
Index 7 outside the range of the array
Index 8 outside the range of the array
Index 9 outside the range of the array
0 10 20 30 40 Index 5 outside the range of the array
Index 6 outside the range of the array
Index 7 outside the range of the array
Index 8 outside the range of the array
Index 9 outside the range of the array

没有 （！）：

Error access message..
Index 0 outside the range of the array
Index 1 outside the range of the array
Index 2 outside the range of the array
Index 3 outside the range of the array
Index 4 outside the range of the array
0 10 20 30 40 Index 5 outside the range of the array
Index 6 outside the range of the array
Index 7 outside the range of the array
Index 8 outside the range of the array
Index 9 outside the range of the array

有人可以向我解释在这种情况下运算符 （！） 究竟是如何工作的吗？为什么需要它，它如何影响方法？