The this keyword-javaTutorial-php.cn

The this keyword

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Release： 2024-08-02 07:40:03

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A palavra-chave this

Definition of this:

this is a reference to the current object that invokes a method.
It is automatically passed to all methods of a class.

Use of this within methods:

Allows you to access members (variables and methods) of the current instance.
this is optional when there is no ambiguity, but necessary to differentiate between local and instance variables with the same name.

Example without this:

class Pwr {
    double b;
    int e;
    double val;

    Pwr(double base, int exp) {
        b = base;
        e = exp;
        val = 1;
        if (exp == 0) return;
        for (; exp > 0; exp--) val = val * base;
    }

    double get_pwr() {
        return val;
    }
}

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Explicit use of this:

Clarifies code and resolves ambiguity.
Example of use to resolve name ambiguity:

class Pwr {
    double b;
    int e;
    double val;

    Pwr(double b, int e) {
        this.b = b;
        this.e = e;
        this.val = 1;
        if (e == 0) return;
        for (; e > 0; e--) this.val = this.val * b;
    }

    double get_pwr() {
        return this.val;
    }
}

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When to use this:
Useful for accessing instance variables when names conflict with local variables or parameters.
In constructor methods, to reference the object under construction.

class Pwr {
    double b;
    int e;
    double val;

    Pwr(double base, int exp) {
        this.b = base;
        this.e = exp;
        this.val = 1;
        if (exp == 0) return;
        for (; exp > 0; exp--) this.val = this.val * base;
    }

    double get_pwr() {
        return this.val;
    }
}

class DemoPwr {
    public static void main(String args[]) {
        Pwr x = new Pwr(4.0, 2);
        Pwr y = new Pwr(2.5, 1);
        Pwr z = new Pwr(5.7, 0);
        System.out.println(x.b + " raised to the " + x.e +
            " power is " + x.get_pwr());
        System.out.println(y.b + " raised to the " + y.e +
            " power is " + y.get_pwr());
        System.out.println(z.b + " raised to the " + z.e +
            " power is " + z.get_pwr());
    }
}

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Explanation:

The Pwr class calculates the power of a number.
The use of this is demonstrated to reference instance variables when the method parameters have the same name.

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