Null Pointer Exception in Java

public class Main{

    // returns sum of two numbers
    int sum(int a , int b) {
        return a + b;
    }
    public static void main(String[] args) {
        Main m = null;  // intitialised the object with null value
        // Invoking the method sum on the null object.
        System.out.println(m.sum(10, 20));
    }
}

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public class Main{
    int val = 10;
    public static void main(String[] args) {
        Main m = null;  // intitialised the object with null value
        // It tries to read the data on the null object
        System.out.println(m.val);
    }
}

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public class Main{

    // the java integer class in given here
    int meth(Integer x){
        return x.intValue();
    }

    public static void main(String[] args) {
        // creating a the object m
        Main m = new Main();

        // trying to invoke the method using the null parameter
        System.out.println(m.meth(null));

    }
}

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public class Main{
    // The array arr is set to null
    int arr[] = null;
    public static void main(String[] args) {

        // a object m of type Main is created
        Main m = new Main();

        // trying to print the lenght of the null array
        System.out.println(m.arr.length);

    }
}

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public class Main{
    // The static variable val of type String is set to null
    public static String val = null;
    public static void main(String[] args) {

        // Trying to enter to the synchronized block by using val
        synchronized(val) {
            System.out.println("Synchronized");
        }

    }
}

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class Student {
    String name;
}

public class Main {
    public static void main(String[] args) {
        Student student = null; // No object assigned
        if (student == null) {
            System.out.println("Student object is null");
        }
    }
}

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public class Main{
    public static void main(String[] args) {
        // the string value is initialized to null
        String s = null;
        try{
            // we are checking if the string is equal to "hello" or not
           // if the string is found to be null, then the  NullpointerException will be thrown
            if(s.equals("hello")) {
                System.out.println("The string is \"hello\"");
            }
            else{
                System.out.println("The string is not \"hello\"");
            }
        }
        catch(NullPointerException e){
            System.out.println("NullpointerException");
        }
    }
}

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public class Main{
    public static void main(String[] args) {
        // the string value is initialized to null
        String s = null;
        try{
            // we are checking if the string is equal to "hello" or not, by invoking the equals method from the literal "hello"
            if("hello".equals(s)) {
                System.out.println("The string is \"hello\"");
            }
            else{
                System.out.println("The string is not \"hello\"");
            }
        }
     
        catch(NullPointerException e){
            System.out.println("NullpointerException");
        }
    }
}

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public class Main{
    // method getString() returns the string argument
    public static String getString(String s) {
        // if the string is null it informs the calling method that the argument is illegal.
        if(s == null)
        throw new IllegalArgumentException("The argument is null");
        return s;
    }
    public static void main(String[] args) {

        String s = null;
        try{
            // It throws an IllegalArgumentException
            System.out.println(getString(s));
        }
        catch(IllegalArgumentException e) {
            System.out.println("IllegalArgumentException");
        }

        s = "Hello there!";

        try{
            // It prints the string
            System.out.println(getString(s));
        }
        catch(IllegalArgumentException e) {
            System.out.println("IllegalArgumentException");
        }

    }
}

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public class Main{
    public static void main(String[] args) {
        String s = null;

        // as s == null, it initializes the variable with the empty string
        String ans = (s == null) ? "" : s;
        System.out.println(ans);

        // as the s != null, it initializes the variable the variable with the whole string.
        s = "hello there";
        ans = (s == null) ? "" : s;
        System.out.println(ans);
    }
}

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