正确的变量初始化和从另一个类调用

Question

I have these two examples below:

Example 1:

public class class1{
    private classN var1;
    public class1(param1) {
        var1 = new classN(param1); //here I initialize var1;
    }

    public void setVar1(param1){
        this.var1 = new classN(param1)
    }

    public classN getVar1(){
        return this.var1;
    }
}

public class class2{
    private class1 c1;
    public class2(param) {
        this.c1 = new class1(param);
    }

    public void handle(){
        c1.setVar1(sth);
    }
}

example 2:

public class class1{
    private classN var1; //var1 not initialized inside constructor
    public class1() {}

    public void setVar1(param1){
        this.var1 = new classN(param1);
    }

    public classN getVar1(){
        return this.var1;
    }
}

public class class2{
    private class1 c1;
    public class2() {
        this.c1 = new class1();
    }

    public void handle(){
        c1.setVar1(sth);
    }
}

I want to ask 2 things:

1. Are both examples equal?
2. Is var1 initialized in both two cases or I will get some kind of exception in example 2?

Thank you in advance.

Answer 1

1. No, both examples are not equal. In example one the variable is initialized at construction time and class1 cannot be instantiated without it. In example 2, the variable is not initialized and is given the default value of null until it is set at some later time setVar1
2. No, you will not get an exception. If you try to call getVar1 before you call handle , you will get the default null value.

Answer 2

Are both examples equal?

No, In case -1 , new class1(param); initializes var1; ( to a non-null value), in second case, var1 will be null .